Validity of Reversible Flow Lanes between Kandy Road Flyover and New Kelani Bridge Roundabout along A01 to Accommodate Peak Traffic Flows

This paper examines ways of enhancing road capacity by improving lane efficiency along Colombo-Kandy Road (A01) at Colombo city entrance by introducing reversible traffic flow lanes between Kandy road flyover at Pattiya junction and New Kelani Bridge roundabout, to cater for peak traffic flows. A traffic study was conducted between Pattiya junction and New Kelani Bridge roundabout to find out the benefits and any losses, if reversible traffic flow lanes are introduced along this stretch of road during peak traffic flows in mornings and evenings. Two options of lane assignment were considered for the heavy flow direction during peak hours. Option ( i ) by adding one extra mixed traffic lane towards the heavy flow direction while reducing a lane from the opposite direction, and option ( ii ) adding an additional lane exclusively for buses towards the heavy flow direction while reducing a lane in the opposite direction. These two options were considered for both morning and evening peak traffic flows. By using Davidson’s model the benefits or any losses in travel time was computed for the two options separately for both directional peak traffic flows. The study proved that by the introduction of reversible flow lanes along the considered section, during morning and evening peak traffic flows, the benefits obtained by far outweigh the losses due to minor reduction in road capacity in the opposite directional traffic flows. It was also found that introduction of designated lanes for ‘buses only’ further improves the overall efficiency of the system with higher benefits. If ‘buses only’ lanes are introduced it is of the utmost importance to implement these lanes only for buses, as expected.


Introduction
Colombo -Kandy road (A01), is one of the main arterial roads of Sri Lanka radiating from Colombo, which carries traffic travelling towards the central hills as well as northern and north central areas of the country.Hence, this is one of the busiest roads in Sri Lanka which links Colombo with other major areas of the island.The inbound traffic towards Colombo is very heavy during the morning peak hours near the city entry, and severe congestion of traffic is experienced during the week days (Figure 1).Similar conditions are observed during evening peak hours on weekdays in the outbound direction.This traffic congestion costs the state dearly by means of increased travel time, fuel wastage, vehicle wear and tear, loss of safety, pollution of air and noise etc.It is observed that during peak flows, the traffic towards the heavy direction is extremely heavy, but in the opposite direction the road space is not utilised effectively (see Figure 1).Hence, this study intends to investigate the benefits that could be reaped by introducing reversible or contra flow traffic flow lanes.

Reversible Traffic Flow Lanes or Contra Flow Lanes
In busy arterial roads, when the movement of traffic is very heavy in one direction during a certain period of the day, and also becomes very heavy in the opposite direction during another time of the day, this phenomenon is commonly termed as 'tidal flow'.As a solution to address the tidal flows reversible lanes can be introduced.A reversible lane is one, where the direction of traffic movement is changed according to the intensity of traffic flow in a particular direction (Kadiyali [1]; Salter & Hounsell [2]).

Traffic Data Collection
A manual classified traffic count was performed for 16 hours at a location at 1 km south of Pattiya junction flyover (i.e.towards Colombo) on a normal working day from 6:00AM to 10:00PM.Two-directional traffic was recorded separately at 15 minute intervals at the counting location for 7 different categories of vehicles.
The seven broad categories of vehicles were; three-wheelers, cars & SUVs, all vans, all types of buses, goods carrying vehicles, all vehicles with 3 axles, and vehicle with 4 axles or more as indicated in Tables 1 & 2. The Passenger Car Unit (PCU) factors based on RDA records, for these separate categories of vehicles on flat terrain roads with multiple lanes are indicated in Table 3.  Peak hour average passenger count indicated that, the average occupancy of a bus is around 40 passengers and all other vehicles considered as a mix is around 3.25 passengers per vehicle.These values were used for computing vehicle occupancy in the study.
Figure 3 shows two-directional hourly traffic flows separately, and also the total hourly traffic flow along the considered road section over the counting period from 6:00AM to 10:00PM.

Methodology & Analysis
From the traffic survey results it was identified that the morning peak is from 7:00AM to 8:00AM and the total vehicle volume towards Colombo is around 3050 vph.During the morning peak the total vehicle volume travelling out of Colombo was around 1150 vph (see Figure 3).The total two directional flow was around 4200 vph.
Similarly, the out-bound traffic reaches its peak in the evening between 7:00PM to 8:00PM and the volume is around 2650 vph.During the evening peak the total vehicle volume towards Colombo is around 1300 vph (see Figure 3).The total two directional flow was around 3950 vph, which was less than the morning peak flow.This can clearly be seen in Figure 3.
There are several models available to compute the travel time [3].
( Davidson [4] successfully used the following model to compute travel time differences for varying lane options for urban arterial roads as well as freeways. Where, ttravel time at traffic flow q 0 ttime taken to travel with no other traffic (i.e., zero flow travel time) qtraffic flow (veh/hr/lane) ssaturation flow (veh/hr/lane) y = q/s jlevel of service parameter j is the Level of Service (LOS) parameter which is related to the type of road, road width, frequency of signals, pedestrian crossings, and parked vehicles.Blunden and Black [5] suggest following values for j. j = 0 to 0.2 for freeways j = 0.4 to 0.6 for urban arterials j = 1 to 1.5 for collector roads Hence it is reasonable to assume j = 0.5 for Colombo -Kandy road.ENGINEER 4 Zero flow travel time ( 0 t ) was taken as 2 minutes assuming a desired speed of 60 km/h over the study distance of 2 km with no other traffic.
This study intends to consider several options of lane operations between Pattiya junction and New Kelani Bridge roundabout.This road stretch of 2 km in length (Figure 4) consists of 3 lanes in each direction.To Kandy Direction (PHF 7:00AM to 8:00PM) <-----------  3).Therefore, a 4th lane towards Colombo during this period is found to be beneficial to the system.Similarly, introduction of a 4th lane for out-bound traffic which is above 2000 vph from 5:30PM to 8:30PM (see Figure 3) is also beneficial.

Conclusions
From options (1) & (3), it is observed that benefits can be obtained by introduction of reversible lanes during morning and evening peaks for mixed traffic, to enhance the road efficiency during peak flows.
From options (2) & (4) results it is clear that introduction of designated lanes 'only for buses' will further improve the overall efficiency of the system.If 'buses only' lanes are introduced it is of the utmost importance to reserve these lanes only for buses as expected.To obtain the maximum benefits it should be ensured that buses will not enter the mixed traffic lanes.If this enforcement is neglected it can end up as a failure as shown in [6].
When implementing the reversible flow lanes, careful attention should be paid to the intersection at the turn-off to Biyagama road, and also to the terminal at New Kelani Bridge roundabout to ensure smooth flow of traffic at these critical points.
If the proposed scheme is implemented, one operational advantage is that, since this road stretch is located adjoining the Peliyagoda Police Station, strict implementation is possible with close supervision from the Peliyagoda traffic police division.
It is important that when flow direction is changed in reversible flow lanes, to pay the utmost care by the implementers towards the safety of the drivers during the transition.It is also important that strict lane discipline be maintained by all drivers for obtaining maximum benefits while ensuring safety of all the road users.

Figure 1 -
Figure 1 -Inbound Traffic towards ColomboA newly built flyover above the main railway line at Pattiya junction is of four lanes with two lanes in either direction (Figure2).The distance from the flyover to the New Kelani Bridge roundabout is 2 km.This stretch of 2 km road consists of six lanes in an undivided

Figure 8 -
Figure 8 -Lane Operation Option ( 4 )Davidson's model was applied to compute the benefits or losses of saving on travel time, and then the best options were selected.Computation is summarised in Tables4 & 5respectively for morning and evening peak flows.