Effect of type of road humps on vehicular speeds on residential roads

To reduce potential pedestrian fatalities, in residential road maximum speed is 30km/hour. Apart from installing maximum speed signs, installing road humps may ensure speed reduction. This paper is intended to compare light vehicles and motorcycles speeds and speeds reductions due to road humps. Data collection was done in Modernland, Tanggerang City. Two road segments were observed, i.e. segments with standard and non-standard road humps. Observation was made in morning, noon and afternoon periods. A portable speed gun was used to measure the speed at about 50m and 25m before the road humps. Some mean difference statistical analyses were conducted for both speeds and speeds differences between different type of road humps and between pairs of observation periods. The 0.05 significant level was used. Surprisingly, mean of speeds differences (50m vs 25m) in standard road hump is significantly higher than in non-standard road hump.


Introduction
In residential roads, there are many daily domestic activities, such as, children crosing the roads to reach or return from school, senior citizens walking in the road (where pedestrian path is not available) to get fresh air in the morning, housewives crossing the roads to reach or return from grocery shops etc.To reduce potential pedestrian fatalities due to crash between motorized vehicles, in residential road maximum allowable speed is 30km/hour.Therefore, apart from installing maximum speed signs, installing road humps may ensure speed reduction.This paper is intended to compare light vehicles and motorcycles speeds and speeds reductions due to road humps.Data collection was done in Modernland, Tanggerang City.Two road segments were observed, i.e. segments with standard and non-standard road humps.

Literature reviews
Road fatalities are strongly related with speeds.As understood, kinetic energy when a pedestrian was crashed by a vehicle is half the mass of the vehcile multiplied by the square of the speed.Therefore part of kinetic energy from the speed is incredibly significant.So speed reduction will significantly help fatalities reduction [1]. Figure 1 shows the impact of speed on probability of pedestrian fatalities (accident causing death of road users).It can be seen that due to involvement of speeds in the magnitude of kinetic energy, there are huge increase of fatalities probability from almost zero to beyond 80% if speed is increased from 30 km/hour to 50 km/hour.Speed also determines stopping distance.Figure 2 shows and adaptation of Australian Transport Safety Bureau (ATSB) calculation of stopping distance [2].Again we find benefit or speed reduction, i.e. required stopping distance reduction.For safely stop during driving at 30 km/hour, ones only required less than 15m stopping distance (includes both reaction and braking distance).According to [3], speed limit is 30 km/hour.In Indonesia, road hump is regulated in [4].In Chapter 2 Verse 1, road hump is defined as additional equipment on road which installed to force road user to reduce speed.Road hump should be installed perpendicularly to the road axis with certain width, thickness and gradient.The choice of material for road hump should consider road user safety.
In the same decree Chapter 4 Verse 1 regulate that road hump should be installed in • Roads with construction works According to Chapter 5 Verse 1 of the same Decree, a road sign as shown in Figure 3 should be installed at certain distance before the road hump.This road sign is regulated in [5] on appendix 1 table 1 no.6b.Chapter 7 of [3] regulate the material of road hump can be the same with material of the road, can be from rubber or any other materials with similar effect and should consider road user safety.

Data collection method
Data collection was done in Modernland, Tanggerang City.Two road segments were observed (Figure 6), i.e. segments with standard road hump (Figure 7) and segment with non-standard road humps (Figure 8).Observation was made in morning, noon and afternoon periods.Data Collection for speeds related to standard hump was done twice (Monday, 17 April 2017 and Tuesday 25 April 2017).Data Collection for speeds related to non-standard hump was also done twice (Tuesday, 18 April 2017 and Monday 24 April 2017).A portable speed gun was used to measure the speed at about 50m and 25m before the road humps.The speed gun was operated by a surveyor assisted by another surveyor who recorded the speed data manually.Two types of vehicle were observed, i.e. light vehicle and motorcycle.In each observation period the the length of observation was 60 minutes.Every one minute a pair of speed data (at 50m and at 25m before the speed hump) was observed.It can be either a light vehicle or a motorcycle, whichever measured first at that particular minute.Therefore number of observed light vehicles and motorcycles in each observation period is not equal.

Method of data analysys
All analyses were made seperately for light vehicles and motorcycles.Several mean difference statistical analyses were conducted at significant level of 0.05 to evaluate the followings: 1. Mean difference of speed reduction between vehicles travelling toward standar road hump and non-standard road hump.2. Mean difference of speed reduction between pairs of observation period (morning-noon, morning-afternoon and noon-afternoon) within sthe same type of road hump.3. Mean difference of speed at 50m before standard road hump and non-standard road hump.4. Mean difference of speed at 25m before standard road hump and non-standard road hump.

Results
Table 1 summarizes various speeds related to standard road hump.Table 2 summarizes the same things related to non-standard hump.It can be seen that in general speeds 50m before the standard road hump were higher than speeds 50m before to non-standard road hump both for light vehicles and motorcycles.As the speeds 25m before both type of road humps were about the same then the speeds reductions before standard road hump were higher than speed reductions before the nonstandard road hump for both light vehicles and motorcycles.There is no logical nor theoretical explanation regarding these consistent results.It is also found that motorcycles speeds were higher than light vehicles.It should be noted that all mean speeds (and offcourse maximum speeds) at 50m before any types of road hump were higher than 30 km/hours (beyond the regulation for residential road speed limit).Even the minimum speeds at 50m before any types of road hump were as high as 30 km/hour.Therefore additional road humps might be justified along with additional speed limit sign and public awareness program to reduce speed there.
For further tables on this paper RH stands for Road Hump, SRH stands for Standard Road Hump and NSRH standsfor Non-Standar Road Hump.Table 3 summarizes the mean difference test of speed reduction between standard road hump and non-standard road hump for morning, noon and afternoon observation periods for both light vehicles and motorcycles.It can be seen that all test results were significant at 0.05 and with higher mean of speed reduction for standard road hump meaning that mean of speed reduction for standard road hump is significantly higher than mean of speed reduction for non-standard road hump for all type and vehicles and for all observation periods.Table 4 summarized similar things with Table 3 except that it discuss speeds 50m before the road hump.Table 5 summarized similar things with Table 3 except that it discuss speeds 25m before the road hump.All analyses in Table 4 were significant at 0.05 and although not all analyses in Table 5 were significat at 0.05 but the mean differences were relatively low.The test results in Table 4 and Table 5 correspond with the results in Table 3, i.e. the significant speeds reductions were result of relatively high mean value of speeds at 50m before road hump and relatively low speeds at 25m before road hump.Tables 6 through 8 shows that there were almost no significant mean difference between speed reduction between pair of observation periods (morning-noon, noon-afternoon and morning-afternoon).The original plan of morning period was 06.00-07.00,noon period was 12.00-13.00and afternoon period was 17.00-18.00to describe morning peak hour, noon off-peak hour and afternoon peak hour.However, the survey team misunderstood the instruction and instead conduct the morning period at 10.00-11.00 and afternoon period at 15.00-16.00.These periods of the day might be considered to belong to off-peak hours and this may cause no significant difference of speed reduction.

Figure 1
Figure 1 Impact of motorized vehicle speed to probability of pedestrian fatalities Source: OECD/ECMT Transport Research Centre [2]

Figure 2
Figure 2 Effect of vehicular speeds on stopping distance Source: OECD/ECMT Transport Research Centre [2]

Figure 3
Figure 3 Road sign to indicate road hump ahead According to Chapter 5 Verse 2 of [3], the road hump should be painted with incline white line road markings.Example and dimension of the marking is presented in Figure 4.

Figure 4 Figure 5
Figure 4 Example and dimension of road hump markingsAccording to Chapter 6 Verse 4 of[3], the dimension of Road Hump can be persented as Figure5and regulated as follow:• The shape of road hump is trapezoid • The maximum height is 12cm • The maximum gradient of incline part is 15% • The minimum width of flat part is 15cm

Figure 6 Figure 8 .
Figure 6 Observed segments in modern land indicated with red circles

Table 1 .
Summary of various speeds related to standard road hump

Table 2
Summary of Various Speeds Related to Non-Standard Road Hump

Table 3
Mean Difference of Speed Reduction between SRH and NSRH

Table 4
Mean difference of speed at 50m before RH between SRH and NSRH

Table 5 .
Mean difference of speed at 25m before RH between SRH and NSRH

Table 6 .
Mean difference of speed reduction between morning and noon observation