A THEORETICAL OVERVIEW OF ROAD HUMP EFFECTS ON TRAFFIC SPEED IN RESIDENTIAL ENVIRONMENTS <s> DISCUSSION <s> This literature review contains an overview of the efficacy of various speed reducing measures. Measures that affect driving speed directly are discussed. However, special attention is paid to factors that affect driving speed indirectly, for instance by influencing the willingness to show the appropriate speed behaviour. Advantages and disadvantages of various measures are discussed. Currently, the largest reductions in driving speed are realised by speed reducing measures that physically restrict driving at high speeds. Since this only forces road users to reduce speed, but does not let them choose this voluntarily, a more optimal solution is to design roads that are "self-explaining". By designing a road that provides a speed image, that is in accordance with the actual speed limit, drivers will choose the appropriate driving speed more or less automatically. Currently, subjective road categories do not seem to correspond with the official road categories. Yet, no research has addressed the exact relationship between subjective road classification and actual driving behaviour. (A) <s> BIB001 </s> A THEORETICAL OVERVIEW OF ROAD HUMP EFFECTS ON TRAFFIC SPEED IN RESIDENTIAL ENVIRONMENTS <s> DISCUSSION <s> The paper evaluates the effectiveness of various traffic calming measures from the perspectives of traffic performance and safety, and environmental and public health impacts. The proposed framework was applied to four calming measures – two types of speed humps, speed tables, and chicanes – to demonstrate its usefulness and applicability. A field experiment using probe vehicles equipped with global positioning system devices was conducted to obtain vehicle trajectory data for use in more realistic simulations. In addition, a recently developed vehicle emissions model was used for more accurate evaluation of environmental and public health impacts. The results show that chicane is better than the other types of traffic calming measures considered, except in terms of vehicle emissions. <s> BIB002
It has been widely proven, both through field data and public perception, that road humps are an effective device in controlling the speed of vehicles and ensuring safety for pedestrians and non-motorized road users. Thus a road hump can be installed as a solution for the deterioration of living conditions caused by increased vehicle speeds by causing a visual impression that the road was not intended for high-speed or cut-through traffic. Ibrahim et al. (2003) also identified a linear relationship between average vehicle speed and distance from the hump with an R-squared value of 0.91, indicating that a road hump is significant in reducing the speed of vehicles. The reviewed literatures have sufficiently proven that the road hump profile and spacing are good predictors in determining the effect of a road hump on the reduction of vehicle speeds. As a result, both predictors can be used in further studies in analysing the effectiveness of road humps. The standard speed limit along a residential road in Malaysia with road hump installation is 35 km/h, which drops to 30 km/h near a school. According to Table 2 below, the reviewed literature recommend hump heights of 50 mm -100 mm and lengths of approximately 3 m -4 m to achieve vehicle speeds within the 35 km/h speed limit in Malaysian urban residential area. In accordance with Table 3 , the literature reviewed recommended a hump spacing of not more than 80 m to maintain travel speeds within the 35 km/h speed limit. However this differs from the Malaysian standard as stated by the Malaysian Ministry of Road Works (2012), which identified 100 m as the recommended spacing between humps. Nevertheless the Malaysian standard acknowledges that a set of properly spaced humps can significantly reduce travel speeds. The Malaysian Ministry of Road Works (2012) also added that transverse bars can be installed together with humps if greater speed reductions are required, which concurs with BIB001 statement that transverse road markings or transverse rumble strips can be used to warn drivers of an upcoming hazard and help to reduce speed of the vehicles. It is also interesting that as explained by BIB002 , the effectiveness of an existing device installation can also be assessed by using Roess et al.'s (2004) equation. The equation compares the existing spacing with the value derived for S. In the case that the existing spacing is less than S, it could be assumed that the performance of a road hump would be affected to an extent by any subsequent devices in the traffic calming scheme.  also stated that the equation can be used to determine the minimum distance after passing a traffic calming device. This equation is based on the road's speed limit and minimum driving speed, as below (equation 1). (1) where, V : speed limits, V 0 : minimum driving speed, a : acceleration rate (passenger car acceleration rate is 2.286 m/s 2 ), and S : the resulting minimum spacing between the devices. However, there is a lack of standardization in the construction of road humps throughout Malaysian urban residential areas  . Given the importance of the hump profile and spacing in reducing vehicle speeds, the lack of standardization may reduce the effectiveness of road humps as a traffic calming device and cause discomfort to passengers. Thus further studies should be conducted on the effects of existing road hump profiles and spacing to determine their effectiveness in reducing vehicle speeds and improving the liveability of residential areas. It should also be noted that in addition to the profile and spacing of road humps, some literatures have stated that there are also other factors that need to be considered in analysing the effectiveness of a road hump scheme on vehicle speeds. These factors are namely driver behaviour and the traffic volume along the selected road. The variations observed in driver behaviour upon approaching and accelerating away from the humps have led to inconsistencies in the speeds recorded, and higher traffic volumes will impede drivers from driving at free-flow speeds. The focus on driver behaviour necessitates that the results of a field study be corroborated with the perceptions of residents in the studied residential area, in order to further understand the driver behaviour in their speed selections.