PROBLEM 4 As part of the engineering countermeasures to impr

PROBLEM 4. As part of the engineering countermeasures to improve bicycle safety at intersections, a city has installed bicycle signals at 3 intersections. Before and after the installation a transportation engineer obtained the crash data at these 3 intersections. In addition, she carefully selected 3 intersections as a control sites for each treated intersection. Control sites are very similar to treated sites in terms of traffic and geometric conditions. The number of vehicle-cyclist crashes for each treated and control (non-treated) intersections are provided in the table below. Using the before-after comparison approach, estimate the overall reduction in terms of number of crashes. Treated sites Control sites Crashes Years Crashes Years ID Before After Before After ID Before After Before After 4 2

Solution

Let us determine the reduction of crashes in the treated sites:

ID 1:- No.of crashes before =6

After =5

Reduction of crashes =6-5= 1

ID 2:- No.of crashes before =4

After =4

Reduction of crashes =4-4= 0

ID 3:- No.of crashes before =5

  After =4

  Reduction of crashes =5-4= 1

No.of reduction of crashes for ID 1,ID 2,ID 3 = 1+0+1= 2

In the Control sites:-

In ID a and ID c, there is no reduction of crashes.Then

ID b:-No.of crashes before =7

After =6

Reduction of crashes =7-6= 1

And there is no reduction of crashes ID d.

ID e:-No.of crashes before =4

After =3

   Reduction of crashes =4-3= 1

ID f:- No.of crashes before =4

After =3

Reduction of crashes =4-3= 1

ID g:-No.of crashes before =5

After =4

Reduction of crashes =5-4= 1

There is no reduction of crashes in ID h and ID i.

No.of reduction of crashes for ID b,ID e,ID f,ID g = 1+1+1+1= 4

Overall reduction of crashes= 4+2=6