Within Vision Zero, the thresholds for the amount of biomechanical energy that can lead to serious injury form the basis for determining speed limits. These thresholds have been set by studying the relationship between the probability of sustaining a fatal injury and impact speed for three types of accident:
1 Accidents in which pedestrians are struck by motor vehicles 2 Accidents that involve side impacts between cars
3 Head-on crashes between cars of similar mass
Figure 4 shows smoothed curves for the probability of being killed as a function of impact speed for these three types of accident.
0 10 20 30 40 50 60 70 80 90 100
0 20 40 60 80 100 120
Impact speed (km/h)
Figure 4. Probability of being killed in various types of accident as a function of impact speed. Source Brandberg, Johansson and Gustafsson 1998
The leftmost curve in Figure 4 refers to pedestrian accidents. The probability of being killed when struck by a car increases rapidly when impact speed exceeds 30 km/h. The curve in the middle refers to side impacts involving cars. For this type of accident, the chances of being killed rise sharply when impact speed exceeds 50 km/h. Finally, the rightmost curve applies to frontal impacts between cars of similar mass. It has been assumed that seat belts are worn. For this type of impact, the chance of sustaining a fatal injury rises sharply above an impact speed of about 70 km/h.
Based on these curves, the following classification of roads in Sweden with respect to maximum speed has been developed (Wramborg 1998):
1 Motorways and other divided highways: On motorways and other roads with a high design standard outside built-up areas, a maximum speed of more than 70 km/h is allowed. It is assumed that on these roads there is: (a) a median sufficiently wide to (virtually) eliminate frontal impacts, (b) no roadside obstacles close to the road, (c) no at-grade junctions with other roads, and (d) no pedestrians or cyclists are allowed.
2 Motor traffic roads and 13 metre roads. On these roads, a maximum speed of more than 70 km/h is allowed if there is: (a) a wire guard rail between traffic in opposite directions, (b) guard rails to protect against roadside obstacles, (c) no at-grade junctions with other roads, (d) no pedestrians or cyclists are
allowed. It is assumed that the roads are wide enough to allow three traffic lanes, in an alternating 2 + 1 layout.
3 Minor rural road and major urban arterial road. On smaller rural roads, as well as on major arterial roads in urban areas, a maximum speed of 70 km/h is allowed. There is no median guard rail on these roads. In junctions, the speed limit is lowered to 50 km/h. It is assumed that pedestrians and cyclists who travel along the road are separated by means of at least a safety fence,
vegetation or a sufficiently wide traffic separation area. Crossing facilities for pedestrians and cyclists are assumed to be grade separated.
4 Urban main street. On urban main streets, a general speed limit of 50 km/h is assumed, lowered to 30 km/h at crossing facilities for pedestrians and cyclists.
The layout of urban main streets is characterised by wide pavements and cycle tracks and formal crossing facilities for pedestrians and cyclists.
5 Urban Collector and Residential streets. These are streets with a mixed function, serving partly an access function and partly a collector/distributor function. The streets have mixed traffic and a maximum speed limit of 30 km/h is therefore proposed. Formal crossing facilities do not exist and pedestrians are allowed to cross the road anywhere.
6 Residential street. On pure residential streets, the street has other functions besides just providing mobility. It is a place for people to meet and talk and where children should be allowed to play. This means that driving can only be allowed at walking speed, about 7 km/h. Street layout has to be changed in order to achieve this low speed, by applying suitable speed reducing devices.
Table 6 shows a preliminary classification of public roads in Sweden. It is based on the national road data bank and other sources. The table shows the assumptions that have been made in this report about the amount of traffic, the number of accidents and the number of injured road users on different types of road in Sweden.
Table 6: Classification of public roads in Sweden. Lengths in kilometres. Rounded values.
Mean values for the years 1994-1998
Road characteristics Killed or injured road users Type of road
Speed
limit Length (km) Mean
AADT Mill veh kms Acci-
dents Killed Serious Slight Total
Motorway A 110 1050 19309 7400 446 21 112 547 680
90 290 18895 2000 196 5 33 261 299
70 140 18591 950 260 3 36 349 388
All motorways 1480 19160 10350 902 29 181 1157 1367 Motor traffic road 110 100 14247 520 66 9 27 83 120
90 200 6164 450 75 7 23 88 118
70 70 6262 160 42 1 9 55 65
All motor traffic
roads 370 8367 1130 183 17 59 226 303
Rural 110 110 4180 1675 2555 300 34 130 329 493
Rural 90 90 26410 1890 18215 2613 198 956 3073 4227 Rural 70 70 58680 463 9920 2638 111 786 3059 3956 Total rural 91120 1268 42170 6636 389 2112 7844 10345
Urban 70 70 1700 2949 1830 575 20 148 661 829
State 50 50 6880 1573 3950 1625 39 379 1777 2195 Municipal 50 50 21800 1993 15860 5667 80 1068 5858 7006 Urban 50 50 28680 1892 19810 7293 119 1447 7635 9202
Municipal 30 30 15000 168 920 142 2 31 168 201
Total urban 45380 1362 22560 8010 141 1626 8464 10231 All public roads 136500 2630 64730 14645 530 3738 16308 20576
Other roads 2700 975 24 230 891 1145
4 Current Policies for Road Transport and Road Safety in Sweden
This chapter contains a description of current road transport policy in Sweden.
Policy objectives are presented. As far as road safety is concerned, progress towards current targets is briefly discussed, based on recent trends in the number of fatalities and injuries. The road safety measures that are currently applied are briefly described and an estimate of their potential effects in the years 1994-2000 is presented.