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7.0 FREEWAY "SLIP -OFF" RAMP A preliminary evaluation of a freeway "slip -off" ramp to allow traffic from the north to avoid the local street system and exit directly onto the frontage road or Long Lake Road has been made. Such a ramp would serve many of the trips which have been assumed to use the southbound 135W off -ramp at County Road C. A total AM Peak Hour ramp volume of approximately 400 vph is projected for 1990. In addition to saving travel time for these trips, the slip ramp would divert this many trips away from the Long Lake/County C intersection, which is projected to be the most heavily impacted by the TIF developments and the Rosewood Corporate Center. The southbound thru-trips of 1068 could be reduced with the slip ramp by these 408 trips to only 660 vph, which should have a significant benefit on the capacity of the intersection. From the off -ramp schematic in Figure 7-1, it can be seen that the ramp would, be approximately 800 feet long, and would therefore have a vehicle storage capacity of up to 40 vehicles (or 10% of the expected hourly volume). Typically 10 vehicles per minute would use the ramp and it is unlikely that there would be any queueing problems due to capacity limitations at the frontage road, since cross traffic volumes are estimated to be just over 200 vph northbound and 400 vph southbound. Thus freeway flows are not likely to be impacted. A more detailed traffic flow analysis will have to be carried out to accompany any detailed proposal for the ramp. An additional issue which must be addressed if a slip -off ramp is to be considered is the future of the 135W and TH 280 interchange. Studies are currently underway in the area by MnDOT. A redesign of TH 280 is complete with work scheduled for 1991/1992. Planning for 135W at this interchange is just being initiated and may be scheduled for 1992/1993. Additional analysis of TH 36 is also anticipated by MnDOT. If analysis shows that additional capacity is needed for 135W in this area, .from one to two additional lanes may be needed. This would require a relocation of the TH 280 ramp to the north by from 20 to 30 feet, which could affect the off -ramp as well as part of the Rosewood Corporate Center property, Discussions with staff from both the Minnesota Department of Transportation and the Metropolitan Council suggested that the ramp may have to be thoroughly justified and paid for by non -state funds, since it is unlikely that MnDOT will participate. Support of the City of Roseville for the ramp will also be needed. A detailed review process for the slip -ramp would have to be followed, which is described in Appendix E of the Transportation Chapter of the Metropolitan Development Guide. This is included in this report as an appendix. A number of issues will have to be addressed before the ramp, considered as a freeway interchange, could be approved. The most important of these are outlined in the Appendix, and are discussed briefly here. Of the Interchange Criteria, #4, #5, and #6 are most critical. #4 requires that the need for additional capacity or safety be demonstrated. Some arguments could be made that the ramp will relieve the Long Lake Road/County Road C intersection as well as the local street system. #5 requires that the ramp connect to a minor, intermediate or principal arterial. The connection with the frontage road should satisfy this requirement. #6 indicates that new ramps are not to be provided if the need for additional capacity is justified