Johnnie Ben-Edigbe

Extent of Highway Capacity Loss Resulting from Road Humps

Road humps are traffic calming devices placed across road widths solely as speed reduction mechanism. They include, speed cushions, junction tables, road humps. Whilst it is clear that 75mm deflection like road humps would reduce speed to 20km/h on average, determining their impact on traffic flow rate has often been poorly reported. Based on the hypothesis that on any route with humps mean stream flow will lie within highway capacity loss envelope; moving car observer survey method was used to determine mean stream flows as well as a volumes and speeds of ‘with and without’ road humps sections. The studies were carried out under day light and dry weather conditions so as to eliminate their effects. An important part of the study is employment of dynamic passenger car equivalent values for the road sections. Results show significant highway capacity loss and the mean traffic flows lying within capacity loss envelope. The study concluded that although road humps are effective mechanism for vehicle speed reduction, their resultant highway capacity loss is significant.

Extent of highway travel time differentials resulting from rainfall intensities

Travel time on a roadway segment is what most road users are concerned about. It is a useful guide for measuring road users’ perception of the quality of roadway service. Rainfall affects traffic flows by reducing drivers’ visibility and road surface friction among others. These reductions have profound impacts on travel time. The aim of the paper is to determine the impact of rainfall intensities (slight, moderate and heavy) on travel time. The impact study was carried out at locations along Terengganu East Coast Highway 5, between November 2010 and February 2011. Based on the hypothesis that rainfall intensity has effect on travel time, a ‘with-and-without rainfall impact study for both directions of a single carriageway was conducted. Volume, speed, headway, gaps and types of vehicles collected by way of automatic traffic counter continuously for three months estimated and compared. Rainfall data were collected and supplemented with data supplied by the Malaysian Hydrology Department. Results show that light and moderate rainfall will cause a travel time increase of about 0.43 and 0.54 minutes per kilometer by respectively; whereas heavy rainfall will account for travel time increase of 0.74 minutes per kilometer. It also shows that traffic kinematics and shockwave propagations at the onset of rainfall can also be called to account for travel time differentials. The paper concluded that rainfalls irrespective of their intensities have significant impact on roadway travel time.