Table 2

Main findings of systematic reviews on engineering interventions to improve health through transport

Modes of interventionQuality IndicesMain results
RR, risk ratio; RCT, randomised controlled trial; NS, not significant at p<0.05 level.
Ignition interlock devices440Ignition interlock devices were used for convicted drink-driving offenders. Re-arrest and re-conviction were reduced in intervention versus control groups (RR 0.36–0.85) in a variety of study designs, including an RCT.
Studded tyres341Studded tyres may increase or decrease accident rates, depending on road conditions. 8 included studies found changes in accident rates significant at 95% level: on snow (18–72% reduction), on bare roads (increase of 151% to decrease of 68%), and on all road surfaces (16–57% reduction). Studies with higher quality (large size, surface condition of road specified, type of tyre specified, confounding variables accounted for) showed small, NS effect sizes (2–5% accident reductions). 5 studies on the effects of laws prohibiting the use of studded tyres found increases in accident rates of 3–10% (p<0.05).
Traffic calming schemes642Traffic calming describes measures to discourage non-local traffic from using residential streets and reducing the speed of the remaining traffic. Area wide traffic calming reduces the number of accidents by a mean of 15% in the whole area affected by the measures (main roads and local roads combined). The effects are relatively constant in different countries and in different years.
Daytime running lights443Daytime running lights are associated with a reduction in multi-party accident rates of 14–18% (p<0.05 in prospective controlled studies and in uncontrolled prospective designs, NS in RCTs).
All types of accident (front/side impact, rearend collision, pedestrian, not specified) reduced by 14% (12–16%). There is no clear dose-response relation between proportion of cars using DRLs and accident rates. The effects of DRLs are greater with increasing latitude (for example, 9% reduction in accidents in Israel v 60% reduction in Finland).
Speed limit reductions444Speed limit reductions may be effective on their own in reducing accidents but additional measures may be needed. Speed limit zones in built up areas reduce personal injuries but have no clear effect on material damage. Controlled studies show smaller reductions in personal injuries (18%, 8–26%) than uncontrolled studies (43%, 42–45%). Speed limit zones in quieter peripheral roads are effective in reducing both personal injuries (21%, 9–31%) and material damage (18%, 9–26%). A change to differential speed limits (slower in more built up areas, faster in peripheral roads) is associated with an increase in accidents in the peripheral areas (17%, 0–37%). For 30 km/h zones, accidents are reduced by 3.5% per km/h speed is reduced, independent of study design.
Speed reduction by road humps shows non-significant reductions in personal injuries in controlled studies (37% reduction, 95% CI 67% reduction to 19% increase). Controlled studies show non-significant increases in accidents in areas surrounding road humps. Accidents are reduced by 4.5% per km/h speed is reduced, independent of study design.
Raised crossroads are associated with non-significant increases in personal and material accidents. Rumble strips approaching crossroads are associated with significant decreases in personal (33%, 25–40%) and material (25%, 5–45%) accidents.