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Home My WebLink About1981-02-03; City Council; 6462-1; Intersection spacing on prime arterialsfl -, CITY OF CARLSBAD Initial : Dept. Head AGENDA BILL NO. bc/b;Z- DATE : FEBRUARY 3, 1981 c. Atty v&8 c -- SUBJECT: INTERSECTION SPACING ON PRIME ARTERIALS STATEMENT OF THE MATTER At their meeting of November 18, 1980, the City Council requested a report on the City's Standard for intersection spacing on pr.ime arterials. As the Council is aware, the City's General Plan describes three prime arterials: El Camino Real, Palomar Airport Road and the future Melrose Avenue. Each of the prime arterials will be a six-lane divided highway with limited access. In the past, Council and staff have worked hard to discourage access to these prime arterials except at intersections, and to space intersections at least 2600 feet apart. Recently, Rick Engineering has questioned the City Standard for intersection spacing on prime arterials and has presented arguments for intersection spacing of 2190 feet along Palornar Airport Road. / The City's Traffic Engineering Consultant has reviewed the City Standard and the Rick Engineering input and has essentially concluded that reducing the inter- section spacing on prime arterials could result in reduced levels of seivice (i .e. reduced speed and reduced capacity) . Any reduction in intersection spacing . would require a reduction in travel speed along the prime arterial. Subsequent meetings with Rick Engineering resu ted in a consensus that the existing intersection spacing policy should be retained, with the understanding that instances where topography or access prob ems require closer spacing may occur. e? EXH I B I TS 1. Berryman and Stephenson Report. 2. Weston Pringle and Associates Report 3. Federhart and Associates Report RECOMMENDATION That the Council maintain the current standard of 2600 feet between intersections on prime arterials, with the understanding that instances may occur which could require closer spacing. Council Action: 2-3-81 Council approved the Staff recommendation. MEMORANDUM RECEIVED December 4, 1980 CITY OF CARLSBAD Englnedng Department TO: Les Evans, City Engineer FROM : J, H, Kawamura City of Carlsbad SUBJECT : Intersection Spacing on Prime Arterials DESIGN CRITERIA The design standard for open intersection spacing on prime arterials in the City of Carlsbad is 2,600 feet. The basic purpose of this standard is to ensure a safe and highly efficient flow of traffic on prime arterials. The 2,600 foot spacing criterium has been established in order to effectively: 1. 2. 3. 4. 5. 6. 7. minimize traffic flow interruptions at open intersections and ancillary points of left-turn access to adjacent development; minimize conflicting and/or unexpected turn movements, merging and diverging maneuvers and lane changes; minimize pedestrian crossings and restrict such crossings to signalized intersection; minimize frequency of temporal sight obstructions, and driver distractions caused by intersection cross traffic; minimize accident potential and accident severity; provide uniform intersection spacing for signal coordination and high speed progressive traffic flow; and provide a reasonable and consistent standard for planning and design purposes. ., r- Mr. Les Evans December 4, 1980- Page 2 Based on a design speed of 60 mph (or 55 mph average operating speed), a 2,600 foot intersection spacing strategy allows the "platooning'' of vehicles on prime arterials in increments of approximately 30 seconds (i.e., at a constant speed of 55 mph a vehicle will travel 2,600 feet in 32.23 seconds, or around 30 seconds when allowing for minor fluctuations in speed and acceleration time). The 30 second increment of time is ideal for thepurpose of traffic progression through signalized intersections. Deviating from this time increment would result in poor signal coordination and Ifstop and gof1 traffic conditions. Accordingly, any reduction in intersection spacing (say from 2,600 feet to 2,100 feet) would require a significant reduction in travel speed (from 55 mph to less than 45 mph) in order to maintain progression. Since prime arterials such as Palomar Airport Road and El Camino Real are specifically designed to accommodate high speed travel, it would be unlikely that drivers would voluntarily reduce their speed unless traffic conditions warranted such action. To post lower speed limits would not only be ineffective, but could not be legally enforced. CONSULTANTS! COMMENTS Recently, in two separate correspondences to the Rick Engineering Company (see attached), traffic engineering consultants offered professional opinions on reduced intersection spacing on Palomar Airport Road, a prime arterial, In the first correspondence from Federhart 6 Associates, it was suggested that 2,100 to 2,200 foot spacing should be acceptable since the CALTRANS purportedly allowed the spacing of intersections down to one quarter-mile (1,320 foot) As conceded by the consultant, CALTRANS does not have a "fixed policy" on intersection spacing. In fact, neither the CALTRANS Traffic Manual nor the CALTRANS Highway Design Manual specifies criteria for intersection spacing, Mr. Les Evans December 4, 1980 Page 3 As indicated by the consultant, arterial highways with relatively short intersection spacing can carry high volumes of traffic. However, the consultant fails to acknowledge that on such arterials average operating speeds are quite low (less than 40 mph in most cases). Additionally, in older, established areas, existing land uses and fragmented development necessitates a flexible posture with respect to median openings and intersection spacing on arterial highways. This does not justify relaxing standards in areas where development is just starting to occur, and the opportunity exists to properly provide for long-range traffic needs. The second consultant, Weston Pringle 6 Associates, offers yet another rationale for closer intersection spacing on prime arterials. It is first recognized that the 2,600 foot standard provides for progressive traffic flow, then argued that "capacity" problems can be created at signalized intersections when left- turn demand is heavily concentrated, The consultant concludes that by providing closer spacing ''cycle lengths can be reduced and progressive speeds can be maintained." In general, the operating cycle, phasing sequence and cycle splits of a traffic signal OT series of traffic signals on a high volume arterial have a major affect on capacity. It is highly unlikely, however, that capacity would be significantly affected by left-turn traffic, unless it were indeed extraordinarily heavy and constant throughout the day, The consultant has not demonstratively shown this to be the case - either as an existing condition or by theoretical example. The consultantfs conclusion about closer intersection spacing is illogical if it is based on his discussion of capacity problems. It is a fundamental principle of traffic flow theory, that closer intersection spacing generally results in decreased capacity. Further, it is improbable that a reduction in spacing from 2,600 feet to 2,100 feet would have any significant affect on traffic signal cycle lengths (i,e,, overall traffic demand would remain relatively constant regardless of variances in intersection spacing). Closer intersection spacing would, however, significantly affect the speed of progression, as discussed above. '. -* r" Mr, Les Evans December 4, 1980 Page 4 CONCLUSIONS A reduction in the standard intersection spacing requirement for prime arterials could result in reduced levels of service on Palomar Airport Road and El Camino Real. While traffic is not excessive on these two arterials, it continues to grow with each new development in the area. It is the City's long-range responsibility to provide a circulation system which is responsive and adequate in meeting the needs of the motorist. While minor deviations from the 2,600 foot spacing requirement are to be expected from time to time, because of topographic and/or utilitarian constraints, it would be ill-advised to allow a 500 foot reduction in spacing, In site-specific cases, detailed studies may be warranted in order to determine the significance of any traffic problems created by reducing intersection spacing requirements. The two reports submitted by Rick Engineering's consultants do not technically present a strong case in favor of reduced intersection spacing on prime arterials, However, a more comprehensive analysis might indicate that some measured reduction may be acceptable. ,-I F 4, - ,*. EXHIBIT NO. 2 OF AGENDA BILL NO. 6462 sup 1 w,+lbc 0 I---- - _-__ - __ ____ __ -- ---_- -- TRAFFIC a TRANSPORTATION ENGINEERING Ic)ufoN Pwb acid AM& RICK ENG. Pate RPrPi,d November 14, 1980 NOV 17 1980 Mr. Robert Ladwig Rick Engineering Company 3088 Pi0 Pic0 Drive P.O. Box 1129 Carlsbad, CA 92008 Dear Mr. Ladwig: This letter is in response to your request for our comments relative to the proposed relocation of the College Avenue intersection with Palomar Airport Road in the City of Carlsbad. It is our understanding that consideration is being given to moving College Avenue westerly to align with Laurel Tree Road. This relocation is being proposed to more closely conform to the half mile intersection spacing standard for Prime Major Arterials. It is further under- stood that you have proposed an intersection spacing along Palomar Airport Road of approximately 2100 feet. The half mile spacing of arterials is a criteria that has been developed to allow for coordination of traffic signals while maintaining a progressive traffic speed. speed can be maintained and a 120 second cycle provides a 30 mile per hour speed. It can be seen that these speeds are related to signal cycle lenghts as well as intersection spacings. As examples, with a 90 second signal cycle length a 45 mile per hour As you are sware, our firm has recently analyzed traffic conditions for the Koll project, Rancho Carrillo and Carlsbad Oaks. found indications of potential capacity problems at major intersections along Palomar Airport Road. These potential capacity problems are related to the heavy left turn movements resulting from a limited numbc-r of intersections or opportunities to execute left turns. become longer and the progressive speed is reduced. section spacing, cycle lengths can be reduced and progressive speeds can be maintained. In each of these analyses we have As traffic dcmands increase, cycle lengths By providing closer inter- As an example a 30 mile per hour speed can be maintained with 60 2651 EAST CHAPMAN AVENUE SU!TE 110 FULLERTON. CALIFOF’JIA 92631 (714) 871-2931 I. . .. r-. 4 L I -2- second cycles and one quarter mltc intcrscct ion spocirtg. The planned development along Palomar Airport Road and the area served by this facility will result in increased traffic and a more urbanized area. These conditions have historically resulted in the need for increased road capacity to serve the land uses. there is a need to examine the current standard of the City which relates to one half mile spacing of intersections. spacing has been maintained. Based upon the analyses conducted by our firm and others, We know of no urbanized area where this In summary, we would support your proposed intersection spacing along Palomar Airport Road and encourage the City to re-examine the current standards based upon recent studies of future tra’ffic conditions. We trust that these comments will be of assistance to you and the City. have any questions or require additional information, please contact us. If you Respectfully submitted, WESTON PRINGLE AND ASSOCIATES Weston S. Pringle, P.E. cc: Mr. Bernie Fipp Mr. Timothy Strader WSP : cd 114162 EXHIBIT NO. 3 OF Federhart & Associates 5252 Balboa Avenue, Suite 709 San Diego, CA 92 117 (7 14) 278-3365 November 13, 1980 Rick Engineering Company Mr. Bob Ladwig 3088 Pi0 Pic0 Drive Carlsbad, CA 92008 AGENDA BILL N0.6462 s8: TRAFFIC AND PARKING STUDIES fI0V 14 7980 Dear Bob: - You asked if we would comment on the adequacy of intersection spacing along Palomar Airport Road in Carlsbad -- this is our answer. As I understand it, you want to keep College located where it is proposed in the Signal-Airport Business Center. You would propose moving Bircher Pacific 500 feet farther east to a midpoint between College and Camito Vita Roble. Bircher Pacific would leave about 2100 feet each side of Bircher Pacific to Camito Vita Roble to the east and College to the west. This moving of YOU also said that west of College, if College is left where proposed in the Signal- Airport Business Center, there would be about 2200 feet west of College to Laurel Tree Road. We think this is very good spacing of major intersections along Palomar Airport Road even though we know it is a prime arterial. We must think of service to the land -- if we have too few access intersections, then so much side-street traffic must use each of these side streets that large amounts of traffic-signal green time must be taken from the prime arterial and given to the side street in order to accommodate side-street traffic. street spacing so that the main street can have as much green time on the signals as possible. To illustrate in this case that the 2100-to2200-foot spacing is reasonable, a check with CalTrans reveals that on their expressways, though they have no fixed policy, they do allow intersections down to 1/4-mile spacing (1320 %t) and prefer a minimum of 1/3 mile (1760 feet). from the 2100 to 2200 we are talking about. We think it is better to have reasonable side- As can be seen, either of these 1s a long way To illustrate six-lane street traffic carrying capability, we only have to look in San Diego on Balboa at 1-805, where this street is carrying 50,200 ADT with all kinds of closely spaced signalized intersections. Another six-lane street with all kinds of side street intersections and driveways is Harbor Drive near Lindbergh Field, which is carrying an ADT of 67,400. i 0 Rick Engineering Company .IT 8084 -2- November 13, 1980 We think the above paragraphs illustrate that 2100-foot spacing along Palomar Airport Road is very adequate. m:vc E