Part VII: ADDENDUM 2: TRAFFIC AND TRANSPORTATION ENGINEERING
This addendum presents the findings and recommendations of a traffic study conducted by Kimley-Horn and Associates, Inc. for the proposed Las Colinas Urban Center Transit Oriented Land Use Plan. In April of 1991, the consulting firm of DeShazo, Starek & Tang, Inc. performed a traffic study for the City of Irving analyzing the roadways into and out of the Las Colinas Urban Center.
The 1991 City of Irving report concluded that to accommodate the proposed development the traffic generated from the Las Colinas Urban Center land use plan would have to be scaled down by 13%. Also, this study showed regional roadway impacts from development and how the Urban Center is impacted by those external trips. Upon completion of this study, a comparison was made between the RTKL Transit Oriented Land Use Plan trip generation and the 1991 development plan. The results of the analysis shows that the new land use plan produces an 18% reduction in daily trips, which eliminates the 13% shortfall identified in the 1991 City of Irving report. The following memorandum describes the methodology that was used, trip generation results, segment analysis and finally conclusions and recommendations. For additional information regarding transportation options and details refer to section 5.1.2.
The findings and methodology of the 1991 City of Irving report were reviewed to identify traffic assignment patterns, trip generation rates, and previous build-out scenarios. These findings were used in conjunction with the proposed land uses from the RTKL Land Use report to document the traffic impacts within the Las Colinas Urban Center. As such, the development schedule has been updated since completion of the 1991 City report; accordingly, the most current development schedule is applied in this report. Figure 1 shows a development program consistent with the proposed RTKL Land Use plan.
Using the trip generation rates, distribution, assignment patterns and background development proposed in the 1991 City report, KHA added the new land uses from the proposed RTKL Land Use report and evaluated the overall traffic impacts to the Las Colinas Urban Center.
Trip Generation rates were generated from population and employment data supplied by the North Central Texas Council of Governments (NCTCOG). The rates are also consistent with the 1991 City of Irving Report. The trip rates are shown below.
In addition to using established trip rates, a 5% internal capture was used to eliminate those vehicles that visit two or more different land uses during the same trip. The trip generation calculations resulting from the proposed land use scenarios are shown in Figure 1.
With light rail stations located within the Las Colinas Urban Center, several mode-split options were generated for various modes of transportation, i.e., carpooling, vanpooling, bus or rail, and even walking. A range of reduction factors from 0% to 25% was applied to the roadway segments after the trips were distributed. Background traffic volumes, supplied by the City of Irving, were factored 1% annually for 20 years, to produce a year 2020 background traffic data set. Expected traffic generated by the urban center was then added to the 2020 background volumes to produce a total build-out of the Las Colinas Urban Center.
Roadway Network & Level of Service Analysis
The Texas Department of Transportation is currently conducting a Major Investment Study for SH 114 and Spur 482. The analysis in this report assumes that the locally preferred alternative for the schematic design will be implemented.
The study links are listed below and shown graphically in Exhibit 1.
Link 1: Las Colinas South of Royal
Link 2: Las Colinas South of O’Connor
Link 3: Las Colinas South of Wingren
Link 4: O’Connor North of Spur 348
Link 5: O’Connor South of Spur 348
Link 6: Rochelle South of O’Connor
Link 7: Rochelle North of SH 114
Link 8: O’Connor East of SH 114
Link 9: Las Colinas North of California Crossing
Link 10: O’Connor East of West Las Colinas
O’Connor Boulevard- is currently a 6-lane divided arterial that provides access to the site from the north and south. The City of Irving Thoroughfare Plan identifies O’Connor Blvd as a 6-lane divided facility. O’Connor Boulevard intersects Spur 348 and the SH 114 Frontage Roads.
Rochelle Boulevard- is currently a north south 6-lane divided facility and runs adjacent to the East Side of sub-areas 3 and 4. The City of Irving thoroughfare plan identifies Rochelle Blvd as a 6-lane divided facility. Rochelle Blvd intersects the SH 114 frontage roads at grade.
Las Colinas Boulevard- forms an inside loop bordered by SH 114 to the west, Rochelle Blvd to the south and east, and Spur 348 to the north. The City of Irving Thoroughfare plan identifies Las Colinas Blvd as a 6-lane divided facility.
Walnut Hill Lane- is assumed extended to O’Connor Blvd as outlined in the City of Irving Thoroughfare Plan. This facility will provide local access to the urban center and an access alternative for traffic from the east. The City of Irving Thoroughfare plan identifies Walnut Hill Lane as a 6-lane divided facility.
Northwest Highway direct connect ramps- are assumed in place for this analysis, as outlined in the City of Irving thoroughfare plan. The City of Irving Thoroughfare Plan shows these ramps lining up with O’Connor Blvd. This analysis assumes the direct connect ramps line up between O’Connor and California Crossing. The direct connect ramps will provide an access alternative for traffic coming from the east.
California Crossing- is currently a two lane divided roadway extending to the east from O’Connor Blvd. This facility is expected to provide local access to the urban center and an access alternative for traffic from the east. The City of Irving Thoroughfare plan identifies California Crossing as a 6-lane divided facility.
Level of Service Analysis
The projected daily traffic volumes expected on the study links when the Las Colinas Urban Center is completely built-out are shown in Exhibit 2. These numbers divided by the capacity of each individual roadway produces the volume to capacity (v/c) ratio, which is used to determine the link’s level of service (LOS).
The critical links in this analysis are O’Connor Boulevard just east of SH 114 (Link 8) and just south of Spur 348 (Link 5). The v/c ratios are 1.17 and 1.15 for Links 8 and 5, respectively; a daily capacity of 49,000 vehicles per day is assumed for O’Connor Boulevard and a 15% trip reduction rate is assumed for the development.
The internal sites in the Sub-area will be accessed through a supporting system of two and four-lane roads which are accessed by the service roads and the Texas Plaza-Century Center Connection. With Sub-area 1, north being bisected by the light rail line, it is necessary to connect for the internal streets to cross the light rail line to provide full access to both areas. At-grade crossings are possible but the vertical alignment of the light rail line may present opportunities for relatively inexpensive grade –separated crossings.
Regional priorities for roadway access and circulation
As development continues in the Urban Center certain critical improvements must occur to provide relief to the existing roadway system. While none of improvements are funded at this time, the work to resolve environmental and intergovernmental issues should begin as soon as possible. The highest priority for implementation should be improvements to Walnut Hill Road. Creating a connection from O’Conner Boulevard to the existing terminus of Walnut Hill Road will provide relief to Spur 348, O’Conner Boulevard and also SH 114. Also, additional capacity for California Crossing will also create more opportunities for regional access and circulation. As identified above, improvements to Spur 348 will also provide additional regional capacity. Listed below are additional conclusions and recommendations that have been identified.
Conclusions and Recommendations
It can be concluded that with planned developments from the 1991 City of Irving report and planned development from the RTKL Land Use plan that there is enough roadway capacity within the Las Colinas Urban Center to handle the intensity of development. The problem links identified in this report can be rectified by improving Walnut Hill Road, Spur 348, California Crossing and providing adequate capacity to the O’Conner / Rochelle intersection.
O’Connor Boulevard just north of the SH 114 interchange and just south of the Spur 348 have been identified as potential problem links in the Las Colinas Urban Center. Construction of additional thoroughfares such as Walnut Hill Road and California Crossing are recommended to divert traffic from O’Conner Boulevard.
The Las Colinas transit mall should be built to accommodate four lanes of traffic, with the option of two of the four lanes providing on-street parking during off-peak periods.
Coordination with TxDOT to provide increased access to the Texas Stadium site and Central Freight site. Investigate the feasibility of an interchange with the new road planned to connect both sites and a possible elevated intersection to have direct access to both Texas Stadium and Central Freight.
Las Colinas Boulevard (east), which is not yet constructed, will be re-platted in a straightened alignment from a T-intersection with Las Colinas Boulevard to O’Connor Boulevard as a transit mall serving light rail and local vehicular traffic. The new name for this important street will address and help form the identity of the new Transit Urban Center.
The intersection of Rochelle Boulevard and O’Connor Boulevard will be reconfigured to a T-intersection with north-south Rochelle-O’Connor forming the continuous route.
O’Connor Boulevard between Las Colinas Boulevard and Rochelle Boulevard will be reduced to four lanes with parking with parking removed in peak hours if necessary.
Cross streets between Rochelle and the transit mall will define development blocks.
TRAFFIC AND TRANSPORTATION ENGINEERING ISSUES
O’Connor Boulevard/ Rochelle Boulevard
The capacity and operations of this intersection are of concern due to the high volumes projected on both facilities and due to the proximity of the light rail grade crossing of O’Connor Boulevard. While more detailed planning and operational analysis is called for, several concepts have been considered. Preliminary analysis indicates that as a component of a total package of street and highway improvements, the O’Connor/Rochelle intersection will be able to function at an acceptable level of service.
The current layout of this intersection has O’Connor Boulevard in a curve where it is intersected by two-lane Rochelle Boulevard. This layout is undesirable because the curve geometry reduces capacity and safety and because it makes it less viable to expand Rochelle Boulevard. Three alternative layouts were considered, all of which eliminate the O’Connor curve and make Rochelle-O’Connor-North the continuous route.
The most basic approach, and the current recommendation, is to create a “T-intersection” with O’Connor South intersecting O’Connor North-Rochelle. O’Connor northbound will be served by dual left-turn lanes and the O’Connor to O’Connor right turn will also be dual. Three-phase signal operation with dual turn lanes will provide the capacity needed for the intersection. Vehicle detection and signal operations will ensure that vehicle queues will not be in conflict with light rail operations at the adjacent intersection.
Another option considered is a modern roundabout. This is an intersection type that facilitates the continuous flow of turning and through-movement vehicles into common lanes (the roundabout). This approach has the advantage of continuous flow (vehicles yield and merge but are not stopped by sign or signal). More detailed analysis might demonstrate that this type of intersection could handle the projected demand at this location; however, the preliminary findings are that the number of lanes involved and the traffic volumes may exceed the capacity of a roundabout.
A grade-separated intersection would provide for the continuous movement of O’Connor North-Rochelle traffic. An at-grade diamond intersection would handle all turning traffic. The capacity of this configuration would easily accommodate the expected demand. This approach is not recommend because of the expense, visual impact of an overpass, and impacts on property access.
A more innovative approach was also considered. High-capacity, two-phase signal operations can be utilized at the intersection if traffic turning from Rochelle Boulevard to O’Connor Boulevard (south) is not present. To accomplish this the Rochelle left-turning traffic turns in advance of the intersection into a left-turn lane that is west of Rochelle, southbound. This type of intersection has been used in a few locations, but not in Texas. Although it has promise in some specific instances it is not recommended because a more traditional intersection is expected to meet demand. The disadvantages of the advance turn approach are that it restricts access and may not meet driver expectations.
Texas Plaza- Century Center Boulevard Connection
This proposed road in Sub-area 1 is proposed to improve access to the site from SH 114, to provide “address visibility” to developments in the Sub-area, and to improve circulation between Sub-area 2, and the two parts of Sub-area 1 that are separated by SH 114. This new facility is recommended as a full-diamond interchange with SH 114 because this is the optimal design to achieve the benefits needed. However, the planning recommendation needs to be subjected to schematic layout analysis to determine what is feasible. The full-diamond interchange will either require several acres of land to accomplish grade changes, or will require that the service roads are elevated to meet the elevation of the new connection. The elevation of the service roads will impact access potential. It may be possible to still have access to the service roads from multistory parking garages. A different type of interchange that also has a significant right of way impact is a full or partial cloverleaf interchange. These typically use more land than a diamond interchange but may provide a higher level of service due to uninterrupted flow characteristics. This type of interchange would be between the service roads and the connection.
If neither approach is feasible the connection may exist without direct ramp access from SH 114. This approach would use the local street connections to provide access between the service roads and the connection. While this will provide connectivity, it is less direct and does not provide the address identity that is advantageous.
Discussion of access and circulation at Spur 348
Spur 348 is envisioned to be a limited access freeway with the frontage roads of the freeway serving local traffic with interchanges at O’Conner Boulevard and Las Colinas Boulevard. Overpasses with Spur 348 at O’Conner Boulevard and Las Colinas Boulevard will be necessary to circulate into and out of the Urban Center. To date, it is undetermined if Spur 348 will go over the side streets or the side streets will go over Spur 348. Ramps west of Las Colinas connecting Spur 348 and Las Colinas Boulevard will be needed to provide access to the proposed development north and south of Spur 348. Additionally, east of O’Conner boulevard a new ramp will be need to access the planned development and to provide a connection with O’Conner Boulevard. As described in the light rail alignment alternative, the rail crossing Spur 348 can either go under Spur 348 or cross the frontage roads at grade, assuming Spur 348 is elevated. The need for theses improvements is identified by the access and circulation problems that will exist.
Discussion of Light Rail and Street Alignment Issues in Sub-area 4
In Sub-area 4 a combination of Alignment A-3 and Alignment B is recommended over Alignment A. The discussion of alternative alignments in Section 3.1 is necessarily brief and does not discuss all of the issues related to Alignment A. This paragraph will address these issues in more detail. Alignment A has the light rail line remaining in a transit mall north from O’Connor Boulevard and turning northwest to run parallel to Spur 348. As it approaches the proposed convention center site and Las Colinas Boulevard West the light rail line would curve to the right to an alignment parallel and adjacent to new Las Colinas Boulevard. The dual tracks for light rail would leave the roadway which continues westward to intersect Las Colinas Boulevard. This diversion of tracks and road presents some operational concerns regarding rail and automobile conflicts.
The area of this curve is just east of the convention center site and the preferred location for a station. There are three potential locations for the station relative to the curve. The first is on the tangent section before the curve. The second and less desirable location is created by “breaking” the curve with a tangent section between two shorter curves. This places the station farther west. The third location is on the tangent between the curve and Spur 348.
The alignment just east of Las Colinas Boulevard must now cross Spur 348. This would occur just east of the diamond intersection with at-grade crossings of both the eastbound and westbound service roads of Spur 348. The crossing control and the traffic signals would be interconnected to let the signals advance to phases that do not conflict with the train. Additionally, “No-turn, Train” signs would be required for Las Colinas Boulevard.
Proceeding north from Spur 348, the light rail line would cross northbound Las Colinas Boulevard to enter the median. As noted earlier, the “flat” angle or skew of the rail line and roadway presents an operational situation that is less than desirable. In summary, the western alignment of the light rail line presents numerous design and operational difficulties related to the convergence of the light rail line, Las Colinas Boulevard, and Spur 348. While the alternative cannot be deemed infeasible at this planning stage, the existence of a more favorable alignment presents a clear choice for the preferred alignment.