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Designing Roads That Guide Drivers To Choose Safer Speeds

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Do the physical characteristics of roads and the roadside environments influence the speed of traffic on those roads? That's one of the principal questions that the Connecticut Transportation Institute looked into in its report, "Designing Roads that Guide Drivers to Choose Safer Speeds," released in November 2009.

The researchers found that roadways with wide shoulders, large building setbacks and residential neighborhoods without on-street parking encouraged drivers to drive faster. Conversely, on-street parking, sidewalks and a downtown or commercial location prompted slower average speeds.

"This finding is not surprising, but these relationships are quite strong in the observed data, and it is a useful result to isolate this short list of factors that are significantly correlated with actual vehicle running speeds," the authors note.

The researchers looked at actual vehicle running speeds at about 300 locations in urban, suburban and rural areas across Connecticut, at locations without horizontal curves or traffic control devices. Only vehicles traveling through the section unimpeded either by leading or turning vehicles were counted in order to get true free flow traffic speeds. Roadway and roadside characteristics were observed, and statistical prediction models were estimated to learn more about how free flow vehicle speed, roadway and roadside characteristics and crash incidence and severity are related.

Drivers generally slow down where the road feels “hemmed-in” or there is noticeable street activity, and they speed up where the road feels “wide open” or street activity is less noticeable, the authors conclude.

"These findings demonstrate that through careful, intentional selection of roadway and roadside design elements, it is possible to influence the running speed of traffic on a road. It appears that drivers indeed take cues from elements of the roadway and roadside environment to decide how fast to drive and these cues are independent of the posted speed limit and other considerations that might be important to the community for reducing speeds," the researchers report.

This report has been add to the Best Practices.

  Designing Roads that Guide Drivers to Choose Safer Speeds