Publication

Bermongevallen in Zeeland: karakteristieken en oplossingsrichtingen

Resultaten van een dieptestudie

Author(s)

Davidse, R.J.; Doumen, M.J.A.; Duijvenvoorde, K. van; Louwerse, W.J.R.

Year

2011

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In deze studie is met behulp van weginspecties en interviews zo veel mogelijk informatie verzameld over alle ernstige bermongevallen die gebeurd zijn in Zeeland in de periode maart 2009 tot en met oktober 2010. Het doel daarvan is inzicht te krijgen in de factoren en omstandigheden die van invloed zijn op het ontstaan en de afloop van bermongevallen. Op basis hiervan kunnen maatregelen worden geselecteerd waarmee vergelijkbare ongevallen in de toekomst kunnen worden voorkomen of waarmee de letselernst van deze ongevallen kan worden teruggedrongen.

Run-off-road crashes in the Province of Zeeland: characteristics and possible solutions; Results of an in-depth study

This report presents the results of an in-depth study of run-off-road crashes in the Dutch Province of Zeeland. In an in-depth study of road crashes all possible information is collected about all aspects of the crash: the traffic conditions, the immediate environment, the road users who are involved, their vehicles, and the injuries that have been sustained by the vehicle occupants. The purpose of the present research is to gain insight in the factors and circumstances that have an influence on the occurrence and the outcome of run-off-road crashes. This will provide a basis for the selection of measures that can prevent similar crashes in future or reduce the injury severity of these crashes.

Run-off-road crashes are defined as crashes in which one of the motor vehicles that are involved runs off the road in the initial phase of the crash. The end position of the vehicle is not important; the vehicle may have come to a stop on the verge, in a ditch, against an obstacle or tree, but it may also have crashed into an approaching vehicle. Therefore, run-off-road crashes are not only single-vehicle crashes or obstacle crashes; they can also be frontal or lateral collisions provided that one of the involved vehicles ran off the road in the initial phase of the crash.

Data gathering

During the period 1 March 2009 to 31 October 2010, all run-off-road crashes were selected that met the following criteria: 1) it occurred on a rural road in the Province of Zeeland, 2) a motor vehicle ran off the road in the initial phase of the crash, and 3) an ambulance was called. A total of 115 run-off-road crashes that happened on 60, 80, 100 and 120 km/h roads and in which a motor vehicle (88% passenger cars) was involved, met these criteria. The majority, 110 of the 115 (96%), were single-vehicle crashes; the driver of the vehicle that ran off the road had not collided with any other road user. In five crashes (4%) another road user was hit. In two cases this was an approaching vehicle, in one case it involved a driver who was travelling in the same direction on an adjacent lane, and in the other two cases the other road users were a pedestrian and a cyclist respectively who were located beside the carriageway.

Together with partners in the region, the Province of Zeeland collected information about all 115 crashes. This was information about the traffic situation at that location by means of a road inspection, information about the drivers who were involved and their behaviour by means of interviews, and information about the possible injury sustained by the occupants, also acquired by means of interviews.

The interviews were held by a social worker of the Foundation Social Work & Welfare Oosterscheldebekken (SMWO). Of all 120 involved road users (including the one pedestrian), 44% were willing to cooperate in the study. With 58%, the willingness to cooperate was higher among the female drivers than among the male drivers (39%). Therefore, more information is available about the crashes in which women were involved. This can somewhat bias the results of this study. Furthermore, the willingness to cooperate was also higher among drivers who were over 75 years of age (100%) than among drivers who were younger (see Table 1).

Characteristic

Drivers cooperating

Sex
                Male
                Female

34   (39%)
19   (58%)

Age
                18-24
                25-29
                30-39
                40-49
                50-59
                60-74
                75 or over

16   (41%)
6   (38)%
9   (45%)
8   (40%)
3   (50%)
7   (47%)
4 (100%)

 
Table 1. Number and percentage of involved drivers who cooperated in the study by means of an interview or a completed questionnaire.
 

Characteristics of run-off-road crashes

When the entire group of 115 run-off-road crashes is considered, these crashes are often seen to occur in the weekend, on an 80km/h road, and in a bend (see Table 2). This is shown by comparison with the distribution of all serious crashes on rural roads in the Province of Zeeland in which at least one passenger car was involved. The driver running off the road is often male (74%). Furthermore, the group of men aged 18 - 24 appears to be overrepresented among drivers running off the road.

Characteristic

Share in the number of run-off-road crashes (percentage)

Sex

Male (74%)

Age driver

18-24 (34%), young males (27%)

Day and time of day

Weekends (45%), weekend nights (17%)

Road type

80km/h roads (53%)

Road situation

Bends (47%)

 
Table 2. Most frequent characteristics of run-off-road crashes.
 

According to the police eleven (10%) of the 115 drivers who ran off the road were under the influence of alcohol (blood alcohol content of more than 0.5‰). Ten of these (91%) were male drivers, five of these (45%) were younger than 30 (all male).

Subtypes of run-off-road crashes

The crash process was analysed in more detail for 59 of the 115 crashes. Insufficient information was available about the other crashes, for example because an interview was lacking. For each of the 59 crashes that were studied in detail, the in-depth team tried to determine the course of events and which factors had played a role in the occurrence of the crash and possible injuries. A distinction was made between factors related to the driver of the vehicle, to the vehicle itself, to the road, and to general conditions at the time of the crash. All relevant factors were selected, as the starting point of the analysis was the assumption that a crash is the consequence of a confluence of events and that multiple factors play a role in the causation of crash and injury.

After all 59 crashes had been described in this manner, the crashes with similar crash processes (comparable combination of contributory factors) were grouped into types of run-off-road crashes. Next, these types of run-off-road crashes were described based on the circumstances in which the crashes had taken place, the drivers who were involved and the contributory crash factors. A total of seven types of run-off-road crashes were identified. In Table 3, the characteristics of these seven types of run-off-road crashes have been summarized. The middle column gives a description of the prototypical scenario for each subtype. This scenario contains the greatest common factor of all crashes of that specific subtype. This means that it is not a real crash, but a description by characteristics of that specific type of run-off-road crash.

The contributory crash factors that are given in the right-hand column of Table 3 are the result of the deliberation of every single crash by the SWOV in-depth team. During these deliberations, all relevant factors were selected that according to the team had contributed to the occurrence of the crash and the injury of the occupants of the vehicles involved. To evaluate the factors relating to the road, the characteristics of the cross-sectional profile were compared with the guidelines that have been drawn up by CROW, the Dutch Information and Technology Platform for Transport, Infrastructure and Public Space. Expressions like ‘too narrow’ and ‘too steep’ are the result of such comparisons. A departure from the guidelines was not necessarily labelled as being ‘wrong’; it is never automatically a crash factor. This was dependent on the entire course of the crash. Similarly, the fact that someone is a novice driver and holds a beginner’s licence, is not sufficient reason to select the beginner’s licence as one of the contributory factors. Driving behaviour and/or vehicle control must also give reason to do so. However, there was not always enough evidence to support this. If there was reason to assume that a certain factor had played a role in the crash, but evidence was not entirely conclusive, doubts about the validity of that factor were reported. In Table 3 this is shown by the margins that are given behind the crash factors. The first (and lowest) figure indicates in which percentage of the crashes the crash factor (almost) certainly played a role. The second percentage also includes those crashes in which there was some doubt about the validity of that specific factor.

Subtype

(number of crashes and their share of the total number of analysed run-off-road crashes)

Description of the prototypical scenario

 

Most frequent crash factors*

Distraction
(n=14; 24%)

A young man or woman, sole occupant of the car, is driving on a narrow 80km/h road and is distracted from the driving task. The distraction can have different forms, e.g. being in thought, changing a cd, or reaching for something on the car floor. Because the driver is distracted, he or she gradually leaves the road or drives straight ahead in a road bend. Once the vehicle drives on the verge, the driver loses control of the vehicle and ends up in a gulley (water channel) or ditch situated at a very close distance from the carriageway. In the crash he or she sustains minor to serious injury (MAIS 1-3).

  • Distraction (86-100%)
  • Limit > category (36%)
  • Obstacle-free zone too narrow (64%)
  • Slope too steep (43-50%)

Temporary inability to react
(n=5; 8%)

A young, or, on the contrary, older driver is driving his car during daylight on a weekday. He falls asleep while driving, or is temporarily unable to react as result of a sudden medical condition like an epileptic fit or acute heart complaints. As a result, the vehicle leaves the road and comes to a halt in a gulley (water channel) or ditch. The driver – also the sole occupant of the vehicle – sustains minor to moderate injury (MAIS 1 or 2).

  • Fatigue (60%)
  • Medical condition (60-80%)
  • Obstacle-free zone too narrow (40%)
  • Slope too steep (40%)

Alcohol as main cause
(n=5; 8%)

On a weekend night, a young male driver who is under the influence of alcohol is driving in favourable road and weather conditions, together with a peer. The driver goes straight ahead in a bend and loses control of the vehicle. The main contributory factor is the reduced fitness to drive. In addition, distraction and/or high driving speed play a role. The driver hits the median or runs off the road and ends up in a gulley (water channel) or ditch. The driver’s injury varies from minor to moderate injury (MAIS 1 or 2). The passenger’s injury is mostly unknown, but was fatal in one case.

  • Alcohol (100%)
  • Speed too high (60%)
  • Insufficient warning for bend (20-40%)

Emotional state of mind
(n=4; 7%)

On a weekday evening, a man gets into his car while he is in an emotional state of mind. It is dark and he drives on an unlit road at high speed. He approaches a bend, but fails to notice or cannot keep control of the vehicle. As a result he runs off the road, goes off a slope and crashes into a tree. The driver – also the sole occupant of the vehicle – sustains minor to serious injury (MAIS 1-3).

  • Emotional (100%)
  • Fatigue/distraction (50%)
  • Speed too high (50-75%)
  • Unlit road (50-75%)
  • Obstacle- free zone too narrow (50%)
  • Slope too steep (75%)

Weather and road conditions
(n=12; 20%)

On a weekday, a man or woman aged between 30 and 50 is driving on a 60km/h road in bad weather conditions. The road surface is wet or dirtied with mud. The driver did not adapt his or her speed to the conditions and runs off the road. The vehicle ends up in a gulley (water channel) or ditch. The driver and his or her occupants sustain minor injury (MAIS 1).

  • Speed too high for conditions (42-67%)
  • Weather conditions (58%)
  • Road surface (dirty or holes) (67%)
  • Obstacle-free zone too narrow (33-42%)
  • Slope too steep (50-58%)

Swerving
(n=8; 14%)

During daylight, a young man or woman is driving a passenger car. He or she sees an animal moving onto the road or notices that an approaching vehicle or a vehicle in front is getting very close. He or she swerves to prevent a collision. This manoeuvre causes the driver to run off the road. The reasons may be, for example, that the road surface is wet, the driver has insufficiently adapted his/her speed and/or that the driver is not yet used to the car that he/she is driving. After having run off the road, the vehicle turns over and ends up in a gulley (water channel) or ditch. Given some exceptions, the driver and his/her occupants sustain no to minor injury (MAIS 0 or 1).

  • Speed too high for conditions (0-50%)
  • New or different vehicle (0-38%)
  • Other road user/animal (63-100%)
  • Verge not forgiving (63%)

Wrong assessment
(n=6; 10%)

On a weekend day, a young man is driving a passenger car in favourable road and weather conditions. He has not much driving experience or he is driving in a vehicle or in an environment that he is unfamiliar with. When he approaches a bend he keeps too high a speed or decides to overtake. He then loses control of the vehicle or has to avoid an approaching vehicle he had not seen. As a result, he runs off the road. His vehicle crashes into a tree. The driver sustains moderate to serious injury (MAIS 2 or 3).

  • Beginner’s licence (33-67%)
  • New or different vehicle (33-50%)
  • Speed too high (33-50%)
  • Tight curve radius (33%)

* The first (and lowest) figure in brackets indicates the percentage of crashes in which the crash factor (almost) certainly played a role. The second percentage also includes those crashes about which there was some doubt about the validity of that specific factor.

 
Table 3. Summary of the subtypes of run-off-road crashes. The percentages refer to the share in the subtype in question.
 

When Table 3 is studied, a number of patterns can be distinguished.

Young drivers

Young drivers mainly appear to be involved in 1) crashes in which distraction plays a role, 2) crashes that occur as a result of an inadequate swerving manoeuvre to avoid another road user or object, and 3) crashes that occur because the driver has incorrectly assessed the traffic situation and, as a result, takes a bend at a speed that is too high or overtakes at a point where it is not wise to do so. The young drivers that were involved in the latter type of run-off-road crashes were mostly young males.

Alcohol, emotions and bends

Another crash type in which mostly – exclusively, rather – men are involved, is the type of run-off-road crash that is mainly the consequence of alcohol use. The drivers involved in this type of crash were not only young males; 40% were older than 30. Eighty per cent of these crashes occurred in or near a bend. This bend was not always announced correctly. A crash could no longer be prevented due to the combination of reduced fitness to drive and the high speed of some of the drivers.

Another type of run-off-road crash that often happened in a bend occurred because the driver did not have his thoughts on the traffic due to his state of mind (personal problems). The bend in which the crash occurred was not clearly visible because it was already dark or growing dark and no lighting was present and/or the bend was not announced correctly. The young men who were driving in an emotional state of mind, were also approaching the bend at a speed that was too high.

High driving speed

In two of the crash types discussed above (alcohol and emotional state of mind) and in the crashes in which the (young) driver did not adequately assess the traffic situation, the driving speed was too high because the driver intentionally went faster than the speed limit. Also in crashes of the type ‘weather and road condition’ high driving speed was an important contributory factor, but here there was no intentional speeding; speeds were rather too fast for the circumstances at that moment. The driver should have adapted his or her speed to the bad weather conditions or the bad road surface at that location, but failed to do so. Relatively many of these drivers were female (42%). A speed that is too high for the current conditions also seems to be a contributory factor in run-off-road crashes that occurred after a crash-avoiding manoeuvre (swerving). However, in those cases there was more uncertainty about the role of the driving speed during the deliberations.

Only crashes on a dirty or bad road surface often occur on 60 km/h roads

The crashes of the type ‘weather and road condition’ relatively often occurred on 60km/h roads. This could be the result of the use of these roads by agricultural vehicles, which increases the risk of soiling and wear of the road surface. It could also be the case that the maintenance regimen for access roads is not as strict as that for distributor roads and through roads. Contradictory is that part of the crashes of the type ‘weather and road condition’ occurred on a 120km/h road that showed signs of wear and that a dirty road surface was also present in the crashes that occurred on 80km/h roads.

Distraction on narrow 80km/h roads

The crashes in which distraction played a role relatively often occurred on an 80km/h road. In the majority of these crashes (seven of the ten ‘distraction’ crashes on 80km/h roads) the narrow cross section seems to have been a contributory factor. Although the official speed limit for these roads was 80 km/h, the CROW guidelines on essential characteristics for the recognizability of roads (CROW, 2004b) indicate that the speed limit should have been 60 km/h. The cross sections are too narrow to give the road user sufficient space for timely correction after a deviating driving course. In addition, the obstacle-free zone is too narrow (CROW, 2004a) to make it possible for the road user to safely come to a stop at a speed of 80 km/h.

General factors in run-off-road crashes

For each category of contributory factors (general, human, vehicle and road), Table 4 indicates which factors most frequently played a role in the total set of 59 analysed run-off-road crashes.

Type of factor

Factors most frequently playing a role in run-off-road crashes
(% of the total number of 59 analysed crashes)a

General factors

 

Darkness (7-19%)

Wet road surface (10-15%)

Factors relating to human

 

Distraction (31-42%)

Speed (27-47%)
- too fast for the conditions (10-25%)
- intentional speeding (17-22%)

Alcohol (19-22%)

Fatigue (17-19%)

Novice driver (10-15%)

Factors relating to vehicle

Tyres (2-7%)

Factors relating to road

Obstacle-free zone too narrow (41-42%)

Slope too steep (34-37%)

Bend: curve radius too tight and/or not announced correctly (15-20%)

Speed limit too high for the road category (14%)

Auxiliary lane/hard shoulder and/or traffic lane too narrow or not present (10-14%)

a The first (and lowest) number in brackets indicates the percentage of crashes in which that factor has (almost) certainly played a role. The second percentage also includes those crashes in which there was some doubt about the validity of that particular factor.

 
Table 4. Summary of the most frequent factors in crashes.
 

Some factors co-occur relatively often. In the total set of analysed crashes two combinations are notable:

  1. alcohol and speeding, and
  2. a narrow obstacle-free zone and a slope that is too steep.

In 60% of the eleven crashes in which alcohol consumption by the driver (most) probably played a role in the crash occurring, “intentional speeding” was also considered to be a contributory factor. In the entire set of 59 analysed run-off-road crashes, alcohol use as well as speeding were found to (most) probably have played a role in 14% of the crashes occurring.

In 42% of the 24 run-off-road crashes in which a too narrow obstacle-free zone (most) probably played a role in the crash occurring, the slope being too steep (steeper than 1:3) was also considered to be a contributory factor. In half of these cases the slope was part of a dike, and in the other half it was the bank of a gulley (water channel) or ditch.

In some combinations of factors (relating to road) the factors do not entirely co-occur by chance. Some of the crashes that were analysed occurred on the same road: there are two roads on each of which three (analysed) run-off-road crashes occurred during the phase of data gathering. The layout of these roads seems to have played a role in this. In the first case, it involves a road with an access road layout (60 km/h), but which has an 80 km/h speed limit. The three drivers who were involved in a run-off-road crash on this road were all distracted from the driving task. After they had run off the road, there was hardly any space to correct for their error as there were both trees and a gulley within the desirable obstacle-free zone, which is 6 meters when the driving speed is 80 km/h.

The second road is a distributor road (80 km/h) with a pavement width that is too narrow to meet the minimum width that is desirable for a 1x2 distributor road (CROW, 2004b). As a result, both lane and hard shoulder are too narrow, which increases the risk of road users running off the road. This risk is increased further because a bend is present with a curve radius that is too tight for an 80km/h road. Despite a narrow semi-hard shoulder, there is little space to correct for the error once a vehicle runs off the road because a downward slope which is too steep lies within the desirable obstacle-free zone.

Injuries and injury factors

Sixty vehicles with a total of 91 occupants were involved in the 59 crashes that were analysed in detail. Of these occupants, 2% sustained fatal injury, and 22% sustained injury with a MAIS of at least 2 (serious road injury). Approximately one third of the occupants (30%) had sustained minor injury (MAIS 1). In addition, 14% of the occupants were known not to have sustained any injury, whereas for 29% of the occupants it was unknown which injury they had sustained in the run-off-road crash or it was not possible to determine the injury severity score.

The most severe injury was caused by crashing into a tree. Five of the seven occupants who sustained the most severe injury (MAIS 3 or fatal) sat in a vehicle that came to a stop against a tree. These five occupants were the driver of the vehicle and did not carry any passengers. Four of the five trees (80%) were situated within the desirable obstacle-free zone. The remaining two occupants with (very) serious injury were in a vehicle that came to a stop against the bank of a gulley. 

The obstacle-free zone is intended to give the road user the opportunity to come to a safe stop at the current speed limit. This zone should not contain obstacles that can cause serious damage to a vehicle and/or injury to the occupants (CROW, 2004a). In 25 of the 59 run-off-road crashes at least one not collision-friendly object was present within the desired obstacle-free zone (see Table 5).

Obstacle

Number and percentage vehicles
(n=60)

Tree

6 (10%)

Slope of gulley/ditch

14 (23%)

Slope (without gulley/ditch)

5 (8%)

Total

25 (42%)

 
Table 5. Obstacles within the desirable obstacle-free zone against which a vehicle has come to a stop or which have played a role in sustaining injury. The proportion is expressed as the percentage of vehicles that were involved in the analysed run-off-road crashes.
 

Another factor that often played a role in sustaining injury is the vehicle occupant coming into contact with the vehicle’s interior when it turned over or rolled over during the crash. In total, 27 of the 91 occupants (30%) travelled in a vehicle that turned or rolled over during the crash. Another 5 occupants were in a vehicle that landed on its side. Half (50%) of these 32 vehicle occupants had an airbag. A little less than half (44%) of these airbags unfolded. Approximately a quarter (28%) of the above-mentioned 32 occupants sustained injury with a MAIS of at least 2 (serious road injury) in the run-off-road crash.

The usage and functioning of the different safety devices also played a role in the prevention of (more) serious injury. For 60% of the car occupants wearing a seatbelt probably reduced the injury severity and for a third of them the airbag probably also made a contribution. For three occupants the use of a child restraint seat probably contributed to a reduction of injury severity. For two motorcyclists wearing a helmet contributed to a reduction of injury severity.

Sixteen car occupants (18%) did not wear a seatbelt. Half of them sustained injury with a MAIS of at least 2 (serious road injury or fatal) in the run-off-road crash. Three of these sixteen were thrown out of the vehicle.

Measures to prevent run-off-road crashes

The previous sections indicated that an obstacle-free zone that is too narrow plays a role in the occurrence of about 40% of the run-off-road crashes and plays an important role in the scenarios of four of the seven types of run-off-road crashes. A not collision-friendly obstacle within the 'obstacle-free' zone created a 'danger zone', and deprived the driver from coming to a safe standstill. An important measure to prevent run-off-road crashes is, therefore, moving or fencing off obstacles that are positioned in the obstacle-free zone. This means that priority should be given to following the guidelines with regard to obstacle-free zones, as described in the CROW Handbook for the safe layout of roadsides (CROW, 2004a). The implementation of other infrastructural measures described in this handbook will also improve safety. Based on the contributory factors that were discussed in the previous sections, the following five measures from the handbook are expected to be the most effective in reducing the number of run-off-road crashes:

  • implement speed enforcement and/or lower the speed limit;
  • apply a profiled, acoustic edge marking or install rumble strips on the hard shoulder;
  • move obstacles to outside the emergency and recovery zone, and preferably also outside the minimally required obstacle-free zone, or remove these obstacles altogether;
  • make slopes, ditches, and banks of gulleys more gentle, and apply round tops and foots;
  • apply safety barriers that lead to lower injury severities than driving into the danger zone.

Each of these measures relates to a crash factor that plays a role in 30 to 40% of the run-off-road crashes in the Province of Zeeland that have been studied in the present in-depth study. For the moving of obstacles it must be noted that in the present in-depth study, the team had the desired obstacle-free zone in mind when selecting the obstacle-free zone as a contributory factor, and not the minimally required obstacle-free zone. To get anywhere close to the above-mentioned 40% of the total number of run-off-road crashes, the objects will therefore need to be placed further from the pavement than the width of the emergency and recovery zone, and also further than the minimally required obstacle-free zone for the design speed at that location.

In addition to the infrastructural measures that are discussed in the CROW Handbook for the safe layout of roadsides, a number of ‘new’ measures has been selected which, in the opinion of the in-depth team, fit the combinations of contributory factors that were identified in the present study. These supplementary measures were selected in a brainstorm session with SWOV experts on different disciplines (infrastructure, vehicle, human behaviour). One of the supplementary measures mainly focuses on the road layout (road factor) and is an elaboration of two measures from the above-mentioned CROW handbook (horizontal alignment and/or improving the delineation of tight bends). The majority of the bends in which run-off-road crashes had occurred (86%), had a curve radius that was too tight for the speed limit (assuming a standard superelevation of 2.5%). Such curve radii must be delineated in accordance with the CROW guideline for the marking and signposting of roads. An inspection of the approach roads indicated that 88% of the tight curve radii were not delineated in accordance with the guidelines. An inspection of tight bends and – wherever necessary – adaptation of the layout and/or marking and signposting is therefore a useful measure to reduce the number of run-off-road crashes in the Province of Zeeland.

The most frequently identified contributory factors which relate to human behaviour are distraction (31%), speeding (27%), alcohol use (19%) and fatigue (17%). In all cases, poor state awareness plays an important role. State awareness is about ‘knowing what you are capable of doing, knowing the dangers of certain behaviour or traffic situations and adjusting your behaviour to allow safe traffic participation’. The state awareness of road users can be improved by public information and education, and by making use of in-vehicle information systems that provide feedback about traffic behaviour or warnings about a slippery road surface or unexpected traffic conditions like a traffic jam or roadworks.

Other measures oriented to vehicle and infrastructure that are expected to reduce the influence of the above-mentioned contributory factors which are related to human behaviour are:

  • transverse ridges on the traffic lane on the approach of a bend (distraction, fatigue and/or speeding);
  • acoustic or haptic signals inside the vehicle that warn when the driving speed is too high for the bend one is approaching (distraction, fatigue and/or speeding);
  • monitoring of the driver’s condition (fatigue);
  • plan of attack for narrow roads (distraction); and
  • young drivers-ISA (speeding).

A more detailed description of these measures can be found in Chapter 5.

A number of the above measures were selected based on the fact that certain human and road related factors or road characteristics often co-occur. Examples are distraction in combination with crashes in curves, and distraction in combination with a speed limit that is higher than what is suitable for that road type, cross section, and the width of the obstacle-free zone. This latter combination indicates that run-off-road crashes in which distraction played a role, can also be prevented by using speed limits that are in accordance with the width of the cross section and the accompanying obstacle-free zone (plan of attack for narrow roads). A suitable speed limit informs the driver about the road user behaviour that is suitable for the layout of road and roadside. At this speed, drivers will have sufficient time to correct for a deviation from their course. Public information can be used to enforce the correct driving speed.

To reduce injury as a consequence of running off the road, and rollovers the following supplementary measures are advised: 

  • cover gulleys and ditches with a cattle grid or use different means to level them out;
  • make airbag and seatbelt (even) more intelligent;
  • prevent abrupt steering with a vehicle system that is yet to be developed and stimulate use of the already developed electronic stability control.

If all the above measures are classified by the phase of the run-off-road crash they are relevant for, this results in the set of measures that is shown in Table 6.

Scope of preventive measure

Description of the measure

Prevent drivers leaving   the road

 

Implement speed enforcement and/or lower the speed limit. (R)

Apply a profiled, acoustic edge marking or install rumble strips on the hard shoulder. (R)

Inspection of tight bends and their delineation. (R)

Apply transverse ridges to the traffic lane on the approach of a bend. (R)

In-vehicle system that gives an acoustic or haptic signal if the driving speed is too high  for the bend one is approaching. (V)

In-vehicle system that monitors the driver’s condition. (V)

ISA for young novice drivers. (V + M)

Public information about distraction in traffic. (M)

Create time and space for correction

Improve drivers’ state awareness (M)

Plan of attack for narrow roads. (R)

Move obstacles to outside the emergency and recovery zone, and preferably also outside the minimally required obstacle-free zone, or remove these obstacles altogether. (R)

Make slopes, ditches, and banks of gulleys more gentle, and apply round tops and foots. (R)

Minimize the risk of serious injury

Apply safety barriers that lead to lower injury severities than when driving into the danger zone. (R)

Cover gulleys and ditches with a cattle grid or use different means to level them out. (R)

Apply wheel clamp construction (type of safety barrier) in bends with a tight curve radius. (R)

Prevent abrupt steering with a vehicle system that is yet to be developed and stimulate use of the already developed electronic stability control. (V)

Make airbags and seatbelts (even) more intelligent. (V)

 
Table 6. Measures for the prevention of run-off-road crashes in the Province of Zeeland. (R = related to road, M = related to man, V = related to vehicle).
 
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