Setting up priority treatment combinations for evaluation of efficiency

The aim of this chapter is to set up priority treatment combinations which worth for detailed examination. Running time is going to be defined as a dependent of the means of priority treatments (E_x), the place (H_x) of priority treatments and the state (volume) of traffic flow (Fx). It is easy to see that the number of combinations are high and not necessary to examine all of them like separated busway with free traffic flow. The point is to be able to demonstrate and evaluate the efficiency of the combined prioritization and be able to select the most appropriate process (treatment) for the given traffic situation.

The input variables can be seen in Fig. 2. in accordance with chapter 2. The segment of day does not appear among the variables as the state of flow implies this parameter.

The use of separated busways (E3) which theoretically allows independent running of traffic interferences is necessary due to the examination of conflicts at intersections.

Right before node segregation (H_cs) has a specified length referring to length for lanes change or for length of permanent congestions. Critical point (Hk) is a segment of the route where usually public transport vehicles congested.

The setup of examination pairs (1-4) is done to be able to demonstrate the effect of a treatment or traffic condition. The comparison based on the current running time (tcur1,2) with its value and deviation (how much is the running time reduced).

The advantages and specialties for each single pair are determined and it is also defined that which kind of intervention’s evaluation they are capable of. Examination of stand-alone treatments (e.g. comparison of each strategies) was not a purpose.

The examination pairs are the followings:

Examination environment of bus lane necessity:

(1)

• Bus lane is the most commonly used priority treatment;

• Efficiency of a curb bus lane (E1sz) needed to be examined because of curbside interferences (e.g. right-turning traffic);

• The more longer implementation (75%) is needed to be able to demonstrate the effects on traffic conditions (total length of implementation is not requisite due to the unnecessity of a bus lane at the beginning or at the end of a route regularly);

• Free- and saturated traffic flow (Fsz ,Ft) should be the basis of comparison.

Input variables Description

Maximizing the number of passage passengers

Means of priority treatments

Segregation right before nodes (specified length)

Hv25

Implemented on 25% of the route Hv50

Implemented on 50% of the route Hv75

Implemented on 75% of the route Along the route

Hv100

Implemented on 100% of the route

Place of priority treatments

(2)

• Critical points mean segments right before nodes or at frequently congested sections (compared with Hv75 which includes the congested sections);

• The implementation costs motivate the examination focusing only at critical segments of the route;

• Another is that bus lanes only at critical point can have harmful effects too if the road traffic is held back so much that the separated section is not reachable by bus;

• Application of the most common state of traffic flow (F_k) is reasonable Examination environment of ‘extended’ bus lane:

(3)

• Examination of bus lane supported by prioritization strategies at nodes is also necessary. The examination shows how can be the achieved savings (owing to a bus lane) kept and how much are the public transport vehicles (also trams etc.) held back at the intersection;

• The basis of comparison is the bus lane supported by signal timing control by bus call (E4b) as the most common strategy (other strategies like E4uo can also be used) ;

• Hcs is the basis of comparison to evaluate passage through the intersection specially (rest of the route is irrelevant in this manner.

All these examinations (1-3) should also be executed to median bus lanes (E1k).

Separated systems (like busways) are avoided from any traffic interferences thus examination with different states of flow is not necessary although examination of conflicts at intersections is reasonable.

Examination environment of conflicts with general traffic at intersections:

(4)

• Hv100 allows to examine specially the effect of conflicts at intersections;

• Saturated traffic flow (Ft) is needed to be able to modeling those who cannot leave the intersection on time (and one of the strategies at nodes).

There are two possible ways to examine dependence of input parameters. In one hand application of traffic simulation programs is an option which include more runs in accordance the stochastic nature of traffic. Simulation can implemented on existing or virtual network. In this case mapping of input variables namely priority treatments (route and node elements), relations (transfers) between separated and general traffic (turning movements and illegal use) for the model has to be as exact as it could be.

(Peter, Basset, 2009) On the other hand use of mathematical methods for travel time prediction (based on historical data) can be applied and compared with simulation results. (Bin Yu, William H.K. Lam, Mei Lam Tam, 2011)

Above all definition of exact value of traffic volume and density in accordance to traffic condition categories is also necessary to be able take into consideration the road traffic more specially. Finding critical points of the route (Hk) and defining length of node segregation (H_cs) based on operator experiences or on typical length of congestions are also significant parts of the examinations. Last but not least all the necessary parameters strategies at nodes like vehicle occupation and time-table dates have to be available.

The expected results are the followings:

• It is expected that efficiency and necessity of prioritization highly depends on traffic flow density (e.g. high number of turning movements) (1).

• It is probable that prioritization besides free traffic flow has insignificant effect on running thus all-time availability of e.g. a bus lane is not reasonable (dynamization in time is necessary).

• Examination of bus lane supported by prioritization strategies is essential due to the possible loss of achieved travel time savings at nodes without support by signal timing strategies. The efficiency highly depends on the prioritization strategies (3).

• Since the implementation of a bus lane only at critical point can also have harmful effects on running time (if the separated section is not reachable) an examination should be done (2).

• Naturally further non-expected correlations can also come up.

5. Conclusions

This paper based on the idea that stand-alone use of priority treatments do not take full advantage of prioritization thus combined use of treatments is reasonable. The aim was - besides to introduce two new prioritization treatments namely reversible bus lane and a strategy minimizing time consumption/passenger - to set up combined procedures which worth detailed examination to be capable of demonstrating and evaluating the efficiency of the combined prioritization through the running time. In the light of results potential is provided to be able to select the most appropriate process (treatment) for the given traffic situation.

Acknowledgments

Kozel, M.: A BRT (Bus Rapid Transit) bemutatása, előnyben részesítési eszközként való megközelítése (Introducing BRT as a priority treatment). Közlekedéstudományi Szemle (Scientific Review of Transport), 59 (3), 45-54, 2009. (in Hungarian)

Polgar, J., Tettamanti, T., Dr. Varga, I.: Utasszám alapú forgalomirányítás városi, jelzőlámpás csomópontban (Signal timing based on maximalization of passage passengers). Közlekedéstudományi Szemle (Scientific Review of Transport), 61 (6), 30-37, 2011. (in Hungarian)

Bin Yu, William H.K. Lam, Mei Lam Tam: Bus arrival time prediction at bus stop with multiple routes.

Transportation Research Part C, 19 (6), 1157-1170, 2011.

Peter, T., Basset, M.: Application of new traffic models for determine optimal trajectories. International forum on strategic technologies, October 21-23, 2009.

The analysis of Reversible Lanes Systems on large