ID: 18-02596
Syed Omar Ballari, Pranab Kar, Mallikarjuna C., Department of Civil Engineering, IIT Guwahati, ᶧContact:
[email protected]
INTRODUCTION
METHODOLOGY
• 1965 US Highway Capacity Manual (HCM) introduced the concept of passenger car equivalent (PCE) to measure the impact of heavy vehicles on traffic stream operations. • PCEs are widely used to represent the mixed traffic stream, India is no exception.
RESULTS
Since the traffic stream contains multiple types of vehicles, Sumner et al.’s approach was used. Steps involved are: Generate Passenger car only stream (Base stream) curve using CA based simulation model Generate curve for the mixed stream containing all vehicles excluding the type for which PCE is to be estimated (subject vehicle)
Figure: PCEs of HMV, MThW, & MTW with SD & AO on 4-lane (left) & 6-lane (right) divided roads
Validation of PCEs
Generate curve for the actual traffic stream (termed as subject stream) Figure: PCE Estimation Process
Select the flow values corresponding to the same performance (Figure)
Calculate PCE value of any subject vehicle using 𝐸𝑠 = Figure: Heterogeneous Traffic on Highways in India
Figure: Homogeneous Traffic in Developed Countries
1 𝑞𝐵 ∆𝑝 𝑞𝑆
−
𝑞𝐵 𝑞𝑀
+1
Δp = % of subject vehicles present in traffic, & qB, qM, & qS are base, mixed & subject stream flows at equal performance measure.
Why is it important? • For planning, design & operational analysis of highways. How? • In planning/design, objective is to calculate no. of lanes for a particular level of service (LOS). • This is achieved by knowing demand & service volume.
• Service volume is calculated based on the Figure: LOS of Base Speed-Flow Curves passenger car only traffic stream (by using PCEs related to a LOS). • In operational analysis, goal is to determine prevailing LOS of an existing highway.
OBJECTIVE & SCOPE • To provide a systematic procedure for the PCE estimation of heterogeneous no lane-disciplined traffic stream, moving on multilane rural highways. • Applicable to divided rural highways passing through flat terrains. • Applicable to longer stretches of rural highways with no road side activities.
Requirements of this method: • Selection of performance measure • Development of macroscopic relationships using simulation model
Selection of Performance Measures 𝑁 𝑖=1 𝑡𝑖 ×𝑎𝑖
• AO = ; ti = occupancy time; ai = area of road space 𝑇×𝐴 occupied by vehicle i during time ti (m2); A = area of detection zone (m2); T = total observation period • SD =
• Actual fhv =
𝑞𝑏
𝑞𝑠 ;
qb = flow in base stream, qs= flow in subject (actual) stream.
• Estimated fhv = 1 1+𝑝1 ×𝐸1+𝑝2 ×𝐸2+𝑝3 ×𝐸3; p1, p2, p3 & E1, E2, E3 = proportion & PCE values of HMV, MThW & MTW respectively. • Error in fhv = 𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑𝑓ℎ𝑣−𝐴𝑐𝑡𝑢𝑎𝑙𝑓ℎ𝑣
𝐴𝑐𝑡𝑢𝑎𝑙𝑓ℎ𝑣
TABLE: Error Values of PCEs
• Area Occupancy (AO) & Speed Drop (SD)
𝑓𝑟𝑒𝑒−𝑓𝑙𝑜𝑤 𝑠𝑝𝑒𝑒𝑑 − 𝑠𝑝𝑎𝑐𝑒 𝑚𝑒𝑎𝑛 𝑠𝑝𝑒𝑒𝑑 𝑓𝑟𝑒𝑒−𝑓𝑙𝑜𝑤 𝑠𝑝𝑒𝑒𝑑
• Error in PCE estimation is obtained using the error in heavy vehicle adjustment factor (fhv).
× 100 Figure: Speed-flow curve with SD as performance measure
• At equal SD, it was assumed that both streams will experience similar LOS (Figure).
Developing Macroscopic Relations • For simulating rural highways, Cellular Automata (CA) model developed by Pal & Mallikarjuna (2017) for the Indian traffic conditions was selected. • Flow-performance measure relations were obtained by fitting the speed-density model through simulated data. • PCEs of heavy motorised vehicle (HMV), motorised two wheeler (MTW) & motorised three wheeler (MThW) were estimated.
IIT Guwahati Transportation Systems Engineering
Percentage Error
Speed Drop (%)
4-lane Road
6-lane Road
0 10 20 30 40 MAPE
2.27 2.33 4.88 3.70 2.50 3.14
1.59 3.43 4.91 5.60 5.87 4.28
Area Occupancy (%) 0.01 0.02 0.03 0.04 0.05 MAPE
Percentage Error 4-lane Road
6-lane Road
3.57 2.38 2.38 1.19 0.00 1.90
2.24 1.99 2.37 2.22 2.67 2.30
CONCLUSIONS
• Both the approaches provide similar results but AO provides slightly better result as compared to SD. • The impact of HMV is not much higher compared to the passenger car. This finding is contradictory to the findings of previous studies.
REFERENCES
• Sumner, R., D. Hill, and S. Shapiro. Segment passenger car equivalent values for cost allocation on urban arterial roads. Transportation Research Part A, 1984, 18(5/6), pp. 399-406. • Pal, D., and C. Mallikarjuna. Modelling of Lateral Gap Maintaining Behaviour of Vehicles in Heterogeneous Traffic Stream. Transportation Letters, 2017, pp. 1-9.
