In order to compare the Interchange alternatives and select the design that best satisfies the purpose and needs of the project, the team used Caltran’s Weighted Decision Matrix. The Weighted Decision Matrix allowed the team to compare the alternatives against specific categories with varying degrees of weights.
As seen from the chart below, the team chose to compare the three alternatives against eight categories: circulation, environmental impacts, adaptability, benefits/cost, implementation, socio-economic impacts, user expectations, and aesthetics. Each of the categories have varying degrees of weights based on the team’s perception of their importance. Local circulation was the most important factor as all four of the project’s needs were focused around alleviating congestion, providing greater access for all users, and providing greater mobility. Thus, this category received the full weight of 9. Environmental Impacts were rated the second highest, with a weight of seven, because each category had a varying level of impact on previously undisturbed land. Therefore, it was assigned a weight of 7. Adaptability was rated the third highest because the area is growing rapidly and any Interchange design will need to be considered with future development and growth in mind. Therefore, it was assigned a weight of 6.5. The construction costs of each alternative as well as the benefits that each alternative would generate over a 20-year period were calculated and taken into consideration as the fourth highest category in the Weighted Decision Matrix. This category was assigned a weight of 6. A detailed cost and benefit analysis of each alternative can be viewed in the Cost/Benefit Analysis page of this website. Implementation was rated the fifth highest based on how easy or difficult each alternative would be to construct. This category was given a weight of 5.5. Socio-economic impacts was rated the sixth highest based on how the economy of the local area would be impacted by this project. It was determined that all three of the Interchange alternatives have very minimal impacts on local businesses and residences in the area, leading the team to assign this category a weight of 5. Other minor factors such as user expectations and aesthetics were considered and assigned the weights of 3 and 2.5, respectively.
After assigning weights to each of the categories, each alternative was given a score from 1 to 10 based on how well the team thought that the alternative performed in a given category. For example, for circulation, the Roundabout Interchange provided the most number of intersections with the highest Level of Service, so it was given a score of 10. Finally, each of the scores were multiplied by the weight of their respective categories and in the end, each score was totaled, as shown in the chart below.
As seen from the chart below, the team chose to compare the three alternatives against eight categories: circulation, environmental impacts, adaptability, benefits/cost, implementation, socio-economic impacts, user expectations, and aesthetics. Each of the categories have varying degrees of weights based on the team’s perception of their importance. Local circulation was the most important factor as all four of the project’s needs were focused around alleviating congestion, providing greater access for all users, and providing greater mobility. Thus, this category received the full weight of 9. Environmental Impacts were rated the second highest, with a weight of seven, because each category had a varying level of impact on previously undisturbed land. Therefore, it was assigned a weight of 7. Adaptability was rated the third highest because the area is growing rapidly and any Interchange design will need to be considered with future development and growth in mind. Therefore, it was assigned a weight of 6.5. The construction costs of each alternative as well as the benefits that each alternative would generate over a 20-year period were calculated and taken into consideration as the fourth highest category in the Weighted Decision Matrix. This category was assigned a weight of 6. A detailed cost and benefit analysis of each alternative can be viewed in the Cost/Benefit Analysis page of this website. Implementation was rated the fifth highest based on how easy or difficult each alternative would be to construct. This category was given a weight of 5.5. Socio-economic impacts was rated the sixth highest based on how the economy of the local area would be impacted by this project. It was determined that all three of the Interchange alternatives have very minimal impacts on local businesses and residences in the area, leading the team to assign this category a weight of 5. Other minor factors such as user expectations and aesthetics were considered and assigned the weights of 3 and 2.5, respectively.
After assigning weights to each of the categories, each alternative was given a score from 1 to 10 based on how well the team thought that the alternative performed in a given category. For example, for circulation, the Roundabout Interchange provided the most number of intersections with the highest Level of Service, so it was given a score of 10. Finally, each of the scores were multiplied by the weight of their respective categories and in the end, each score was totaled, as shown in the chart below.
Category |
Weight |
Spread Diamond Rating |
Partial Cloverleaf Rating |
Roundabout Rating |
Spread Diamond Score |
Partial Cloverleaf Score |
Roundabout Score |
Circulation |
8 |
7 |
8 |
10 |
56 |
64 |
80 |
Environmental Impacts |
7 |
10 |
6 |
9 |
70 |
42 |
63 |
Adaptability |
6.5 |
10 |
7 |
5 |
65 |
45.5 |
32.5 |
Benefit/Cost Ratio |
6 |
8 |
10 |
7 |
48 |
60 |
42 |
Implementation |
5.5 |
6 |
10 |
5 |
33 |
55 |
27.5 |
Socio-Economic Impacts |
5 |
8 |
10 |
7 |
40 |
50 |
35 |
User Expectations |
3 |
10 |
9 |
7 |
30 |
27 |
21 |
Aesthetics |
2.5 |
5 |
7 |
10 |
12.5 |
17.5 |
25 |
Value |
Total: |
355 |
361 |
326 |
The team’s final decision was to select the Partial Cloverleaf Interchange with a final score of 361, compared to the Spread Diamond’s score of 355 and the Roundabout Interchange score of 326. The team believes that this choice best satisfies the purpose and needs of the project, provides the best circulation for all users, and provides the most benefits to the community.
