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Location: Tsaritsa Ioanna Blvd - Todor Aleksandrov Blvd,                                       Sofia, Bulgaria

Number of intersections: 15

This case study is an example of Green Traffic Software tool applied to a real urban city arterial. Here we are dealing with one of the busiest arterials in the city, connecting its north-west district with the center. A part of it (9 intersections) is already coordinated though not in an optimal way while the entire arterial is not.

GTS provides multiple coordination schemes for both the part and all 15 intersections together.  What is special about this arterial is that the maximal sum bandwidth is the same (55 s) in both cases. It exceeds the current sum bandwidth (46 s).

Map boulevard Todor Aleksandrov, Sofia

Maps data: Google, © 2023

Input arterial data:

  Number of traffic lights

  Distances between them


  Recommended vehicle velocity


  Split phasing


  Cycle lengths and the desired   common cycle length

Yellow rectangles in the table and on the map highlight the coordinated part of the arterial.

Input arterial data

Data source: Dom Eleshnitsa LtD

Current timing plan by the local Intelligent Transport System:

9 intersections, sum bandwidth 46 s:

The subset of 9 intersections, from 6 to 14, is coordinated, while the entire arterial is not. The time-space diagram of the coordinated subset shows that currently the sum bandwidth is 16 + 30 = 46 s.

Time-space diagram

With GTS, these 9 intersections can be coordinated in a better way, see below.

GTS, 9 intersections, sum bandwidth 55 s:

GTS provides the arterial portrait, showing all possible pairs of bandwidths with 1 sec resolution. In total, 1244 bidirectional timing plans are available, 24 of them provide the maximal sum bandwidth of 55 seconds.

Each green asterisk leads to a particular timing plan: offsets and phase sequences ("orders") are shown together with the time-space diagram. The dark green asterisks mark the bandwidths pairs with maximal sum. The blue circles mark the bandwidth pairs that are impossible in this arterial.

Arterial portrait for 9 intersections

Two TSDs below correspond to the bandwidth pairs marked with green squares. Brown square marks the current coordination scheme.

Inbound bandwidth: 17 seconds

Outbound bandwidth: 38 seconds

Time-space diagram

Inbound bandwidth: 40 seconds

Outbound bandwidth: 15 seconds

Time-space diagram

Now let us turn to the entire arterial. Currently, it is not coordinated at all but the problem can be easily solved with the use of GTS.

GTS, 15 intersections:

For the given cycle length of 110 s we get an arterial portrait containing 19 different timing plans with sum bandwidth 46 s:

Arterial portrait

We get even better solutions by changing the cycle length. Specifically, at C = 108 s the number of available timing plans decreases to 8 but the sum bandwidth becomes the same as that for 9 intersections subset: 55 s.

Two timing plans below correspond to the bandwidth pairs marked with green squares.

Arterial portrait

Inbound bandwidth: 18 seconds

Outbound bandwidth: 37 seconds

Time-space diagram

Inbound bandwidth: 25 seconds

Outbound bandwidth: 30 seconds

Time-space diagram

This study proves that the widespread belief of coordination deterioration with the number of intersection increasing is not always true (read more here).

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