Abstract—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. Index Terms—Vertical deflection, road hump, flow, highway capacity, speed I. INTRODUCTION Road humps are traffic calming (road safety) devices aimed are reducing vehicle speeds. Although they are effective deterrent to speeding motorists, nonetheless they give discomfort to drivers and their passengers because of the need to climb and descend at every installation. Since every road accident prevented is taken as savings, the traveling motorists have accepted albeit reluctantly the discomfort that comes with vertical deflection as a trade off for road safety. Speed cushions take the form of small plateau with gaps between them, making it easier for wider vehicles especially emergency services, trucks and buses to straddle and pass along a route with minimum discomfort. Junction table on the other hand take the form of raised plateau across the entire intersection. They are designed to make it easier and safer for pedestrians to cross the road on the top of the table where speed is lowest. Road hump that is of interest to the study was first introduced in 1970s by Transport Research Laboratory England. Initial research comprised of numerous designs; flat top, round top, heights (12mm – 150mm) and lengths (50mm to 3600mm), as to be expected many failed expectations and dashed hopes. Eventually initial design standards of circular profile hump (3.6m by 100mm height) were installed at trial sites in 1983 and evaluated. Results showed that road humps are effective traffic calming measures [6]. However, the Manuscript received February 10, 2012; revised March 28, 2012. This work was supported in part by grant from the Universiti Teknologi Malaysia Research Management Centre. Authors are with the Universiti Teknologi Malaysia, Skudai 81310 Johor, Malaysia (e-mail: edigbe@utm.my, mnordiana@utm.my). studies have focused mainly on speed reduction in isolation of fundamental parameters. Traffic flow, speed and density on any roadways are related; therefore any one parameter cannot be treated in isolation. Although the result of the studies is conclusive; the analytical approach is questionable. Highway capacity is a central concept in roadway design and traffic control. Headway distribution, bimodal distribution, selected maxima and the direct probability methods are often used to estimate highway capacity. The choice of a particular method depends largely on the data collected and purpose of estimation. According to Highway Capacity Manual (HCM) the capacity of a facility is defined as the maximum hourly flow rate at which vehicles can reasonably be expected to traverse a point or section of a roadway under prevailing traffic, roadway and ambient conditions. Any alteration made to the roadway for example installing a road hump would result in highway capacity loss. Since the highway capacity is an essential ingredient in the planning, design and operation of roadways, it is desirable for traffic analysts to predict fairly accurately the impact of road humps on highway capacity loss. Road humps are used mainly to reduce and control vehicle speeds. Though they are successful in achieving reductions in speed, their usage would trigger highway capacity loss, the extent of which the study is keen to establish. Although not a focus of the study, road humps have been linked to accidents and complaints received by local authorities concerning damage to vehicles and discomfort to motorists. In any case, the study objectives are to; determine whether highway capacity loss will result from road humps and if so, the extent; establish mean stream flows on route with road humps and also whether such flows lie within the capacity loss envelope. In or to achieve these objectives, 75mm road hump installed to TRL 2/96 [4, 5] specifications (see Table I) on a total stretch of 1.2km road was surveyed in Skudai town Malaysia. Skudai is a town is a suburb of the sprawling metropolitan area of Johor Bahru, Malaysia. It is located 16 km from Johor Bahru city centre and very close to Senai International Airport and the Port of Tanjung Pelepas, Malaysia. As often the case with new growth corridors, socio-economic developments also have downside effects, Skudai is no exception. II. ROAD HUMPS In many literatures, pavement distress is taken as potholes, edge subsidence, excessive cracking and un-even road surfaces, often road humps, speed cushions and junction tables are often not considered as pavement distress but vertical deflection. On the contrary, they are all pavement distress. Extent of Highway Capacity Loss Resulting from Road Humps J. Ben-Edigbe and N. Mashros IACSIT International Journal of Engineering and Technology, Vol. 4, No. 2, April 2012 121