Analysis of driver speeds and comfort on horizontal curves in New Brunswick

There are many roadways, often in rural areas, where existing horizontal curves fail to meet minimum geometric design standards for financial or geographic reasons. Posted advisory speeds, set with a ball-bank indicator, are used on these curves to provide valuable information to drivers on what a comfortable speed would be to drive around the curve. The tolerance levels used in conjunction with the ball-bank indicator vary considerably between jurisdictions and many still base their thresholds on studies dating back to the 1930s.;Research recommendations have addressed short-term goals of updating ball-bank indicator threshold levels used for signing to levels that better represent driver behaviour and updating design guide side friction factors to match American design standards, which better reflect driver behaviour. Long-term recommendations addressed undertaking similar studies across Canada to compare driver behaviour between provinces and also the development of uniform signing standards across Canada so that driver expectation will not be violated between jurisdictions.;This study has investigated present-day ball-bank indicator tolerance levels by analyzing actual driver behaviour on 30 curves posted with advisory speeds in New Brunswick. The results indicated that drivers are accepting more discomfort as they navigate curves than is currently assumed which may justify raising the ball-bank indicator threshold levels used for posting advisory speeds. Very low compliance rates were found with posted advisory speeds at the studied sites. Consistency problems between actual posted advisory speeds and policy guidelines as well as between policy guidelines of neighbouring jurisdictions have also been identified. In addition to tolerable ball-bank levels, side friction factors demanded by drivers in New Brunswick were computed using the basic curve equation and found to be well in excess of side friction factors currently being assumed for design.