50 Hampshire Street Cambridge, Massachusetts 02139 tel: 617 452‐6000 fax: 617 452‐8000 June 20, 2012 Mr. Neil Boudreau, P.E. State Traffic Engineer MassDOT – Highway Division 10 Park Plaza, Room 7210 Boston, MA 02116 Subject: Contract #599343, Assignment #2 – Casey Overpass Boston, Massachusetts Peer Review Dear Mr. Boudreau: CDM Smith has reviewed the peer review responses provided by McMahon Associates for the Casey Overpass project dated May 23, 2012. In general, we find that the traffic analysis provided for the Casey Overpass Project has been performed in a professional manner consistent with standard traffic engineering practice and the guidelines of the MassDOT 2006 Project Development and Design Guidebook. The following is summary of our findings from our peer review. General Comments 1. Although the ‘No Build’ alternative is not a viable option, it is recommended that a written summary of Level of Service (LOS) and Queue analysis results for the 2035 No Build condition be provided. Providing a No Build analysis summary will clearly illustrate the difference in LOS and vehicle queuing between the “in‐kind” replacement of the structure (with no network improvements), the at‐grade Build Alternative and the Bridge Build Alternative. This comment has been addressed by McMahon. We have no further comment. 2. Based on our review of the materials, it is our understanding that Synchro was used to determine levels of service and vehicle queuing. Why was SimTraffic or VISSIM not used to obtain levels of service and vehicle queuing as they could provide a better understanding of the traffic operations of the system versus each intersection in isolation? Mr. Neil Boudreau June 20, 2012 Page 2 This comment has been addressed by McMahon. We have no further comment. 3. A table summarizing 50th and 95th percentile queue lengths was provided in the appendix for the existing and the two (2) Build Alternatives. However, the available storage length for each lane group was not specified; the level of impact due to spillback on the adjacent intersections cannot be determined. We recognize that the storage lengths would change between existing conditions and the build alternatives. It is recommended that the available storage be provided for each lane group. This comment has been addressed by McMahon. We have no further comment. 4. It appears the existing conditions were not modeled using VISSIM. Providing an existing conditions model in VISSIM, which can be calibrated based on actual queue lengths in the field, is recommended. This comment has been addressed by McMahon. We have no further comment. 5. It appears that a traffic operations analysis was not conducted at Shea Circle. Although Shea Circle is technically beyond the limits of the project, improvements at this location are key to the entire traffic network. It is recommended that traffic analysis be performed and summarized for this location under Existing, No Build, and Build Alternatives consistent with the surrounding intersections. This comment has been addressed by McMahon. We have no further comment. Existing Conditions 6. The existing conditions traffic volumes on South Street/Washington Street show a significant growth when compared to the 2007 BETA Traffic Study conducted in 2007. On other roadways, the traffic volumes appear reasonable. It is our understanding that the existing conditions traffic volumes were developed by comparing the TMCs with the ATRs and adjusting for any discrepancies. This comment has been addressed by McMahon. We have no further comment. 7. Input traffic volumes in Synchro appear incorrect during PM peak period at the
following intersections:
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Mr. Neil Boudreau June 20, 2012 Page 3 
Arborway On‐Ramp/South Street/N. Washington Street (NB approach) 
Morton St./Courthouse Parking area/Arborway EB Road (EB approach) This comment has been addressed by McMahon. We have no further comment. 8. Use of Peak Hour Factors in Synchro – A default peak hour factor of 0.92 was used at the Arborway Off‐Ramp/South Street intersection (AM peak period only). During the PM peak, actual peak hour factors were utilized. At other intersections, actual peak hour factors were utilized. This comment has been addressed by McMahon. We have no further comment. 9. Use of Heavy Vehicle Percents in Synchro – A default heavy vehicle percent of 2 percent was used at the Arborway Off‐Ramp/South Street intersection (AM peak period only). During PM peak, it appears that actual heavy vehicle percents were entered. At other intersections, actual heavy vehicle percents were entered. This comment has been addressed by McMahon. We have no further comment. 10. Traffic signal timings/cycle length – It appears that the traffic signal timings and cycle length used in the existing conditions analysis does not match the available signal plan information. Were the signal timings/cycle lengths adjusted based on field observations? This comment has been addressed by McMahon. We have no further comment. No Build Conditions 11. Did the CTPS model provide link volumes taking into consideration the mode shift associated with the background traffic growth? This comment has been addressed by McMahon. We have no further comment. 12. How was the mode shift calculated for the eight (8) projects considered in addition to the background traffic growth? This comment has been addressed by McMahon. We have no further comment. Document Code
Mr. Neil Boudreau June 20, 2012 Page 4 13. Input traffic volumes in Synchro appear incorrect during the AM peak period at the following intersections:  Arborway On‐Ramp/South Street/N. Washington Street (NB approach) This comment has been addressed by McMahon. We have no further comment. 14. Use of Peak Hour Factors in Synchro – What is the rationale in increasing the peak hour factors between existing and no‐build at the Arborway Off‐Ramp/South Street intersection (AM peak period only)? During the PM peak, it appears that the existing peak hour factors were utilized. At other intersections, the existing peak hour factors were utilized. This comment has been addressed by McMahon. We have no further comment. 15. Traffic signal timings/cycle length – It appears that the traffic signal timings were adjusted between existing and no‐build conditions. Although No Build conditions typically indicate no changes are made to existing roadway networks and intersection operations, we concur with this approach, as it appears reasonable to expect future timing adjustments provided by Boston Transportation Department (BTD). This comment has been addressed by McMahon. We have no further comment. Build Conditions – At‐Grade & Bridge Alternatives 16. Input traffic volumes in Synchro appear incorrect during the AM peak period under the Bridge Alternative at the following intersection:  Arborway Off‐Ramp/South Street/Washington Street (NB approach) This comment has been addressed by McMahon. We have no further comment. 17. Summary table – Please check the summary table entitled “Capacity Analysis Summary – Weekday Afternoon Peak Hour”; for the Washington Street/Ukraine Way intersection, the letter showing LOS is missing under the Bridge Alternative. This comment has been addressed by McMahon. We have no further comment. Document Code
Mr. Neil Boudreau June 20, 2012 Page 5 Pedestrian and Bicycle Analysis 18. The pedestrian and bicycle growth between existing and future conditions seems higher than the vehicular growth. Please clarify if the CTPS model was used to estimate the growth for non‐vehicular modes. This comment has been addressed by McMahon. We have no further comment. VISSIM Model 19. Was VISSIM utilized solely as a visual tool? There is no summary of Measures of
Effectiveness (MOE’s) using VISSIM provided in the materials.
This comment has been addressed by McMahon. We have no further comment. 20. How were the VISSIM models calibrated for use in future analysis? This comment has been addressed by McMahon. We have no further comment. 21. The following intersections were modeled in Synchro, but were not modeled in VISSIM: 
McBride and Washington (not in Appendix 2 diagram either); 
Bus Lane & Washington Street; 
Tower St and Hyde Park Ave; 
Ukraine Way and Hyde Park Ave; 
Ukraine Way and Washington St; 
Walk Hill and Hyde Park Ave; 
MBTA Repair Facility and Washington St. This comment has been addressed by McMahon. We have no further comment. 22. For signalized locations in VISSIM, detectors are drawn in the files, but they are labeled as “disabled” but there is a call indicated. This comment has been addressed by McMahon. We have no further comment. Document Code
Mr. Neil Boudreau June 20, 2012 Page 6 23. Peak hour factors and % heavy vehicles – many intersections (both signalized and unsignalized) are the default values – However, it appears that for the major study intersections actual values have been entered. This comment has been addressed by McMahon. We have no further comment. Summary While we have identified minor traffic signal adjustments that may be necessary to address as the project advances through the design phases, the traffic analysis provided for the Casey Overpass Project has been performed in a professional manner consistent with standard traffic engineering practices and the guidelines of the MassDOT 2006 Project Development and Design Guidebook. Please call me at (800)‐346‐4946 if you have any questions or require additional information. Very truly yours, Kevin W. Johnson, P.E., PTOE Associate
CDM Smith Inc.
cc: Steve McLaughlin, MassDOT Sharat Kalluri, CDM Smith Lisa Sherman, CDM Smith Document Code