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HomeMy WebLinkAbout7.1 TJKM CrssngGrdStdy CITY OF DUBLIN AGENDA STATEMENT City Council Meeting Date: October 27, _1986 SUBJECT: Silvergate Drive Traffic Study Continued from Meeting of September 22, 1986 EXHIBITS ATTACHED: Report from TJKM RECOMMENDATION: 1) Approve provision of an adult crossing guard on qjfr Silvergate at Amarillo, installation of STOP signs and related pavement markings on Silvergate at Peppertree, and an additional crosswalk on Peppertree. 2) Authorize a budget transfer of $6,300 from Contingent Reserve to cover the cost of an adult crossing guard for the remainder of Fiscal Year 1986-87. FINANCIAL STATEMENT: Annual cost for an adult crossing guard is estimated at $7,200. This includes approximately $1,000 for "supervision." The cost for the remainder of Fiscal Year 1986-87 is estimated at $6,300. Cost of the additional signage and pavement marking is estimated at $1,500. DESCRIPTION: At the meeting of September 22nd, the City Council received a preliminary presentation from TJKM regarding traffic problems on Silvergate Drive and heard comments from many residents of that area. The issues of speeding, STOP signs, and provision of an adult crossing guard for Nielsen School students were discussed, and Staff was directed to continue their study of the problems. TJKM's report, a copy of which is attached, presents the following observations and recommendations. Adult Crossing Guard Additional counts of pedestrians and motorists were conducted, and it was determined that the warrants for an adult crossing guard have been met during the a.m. peak hours. The warrants have been 85% satisfied for vehicles and 60% satisfied for pedestrians during the p.m. peak hours. A survey of Nielsen School parents was made which indicates that enough additional children would walk to school if a crossing guard were provided to completely satisfy the pedestrian warrant during p.m. peak hours. Additional growth in the area will probably create enough traffic to also meet the vehicular warrant in the near future. It is therefore recommended that an adult crossing guard be placed at the intersection of Silvergate Drive and Amarillo Road. An additional suggestion is placement of a crosswalk on the north leg of Peppertree Road at Silvergate in order to direct children toward the crossing guard at Amarillo. STOP Sign Investigation Regarding placement of STOP signs on Silvergate at Peppertree Road, the traffic volume warrant on Silvergate has been met, but the warrant on Peppertree has not. The two accidents which have occurred in the past three years would not have been correctable by STOP signs. Visibility at the ITEM NO. I' er, COPIES TO: TJKM Nielsen School intersection has been analyzed in terms of the speed survey, which indicates that the 85th percentile speed is 36 m.p.h. If traffic were traveling at the posted speed limit of 25 m.p.h., the sight distance at Peppertree would be termed adequate; however, at 36 m.p.h., it is less than the design standard. Therefore, a four-way STOP intersection would benefit northbound traffic. STOP signs would also benefit student bicyclists as discussed below. It is therefore recommended that STOP signs be installed on Silvergate Drive at Peppertree Road. Adoption of an ordinance designating the four-way STOP intersection would need to be scheduled for the next City Council meeting in order to provide a~equat~ notice.. Student Bicyclists A comment needs to be made regarding children who ride their bicycles to and from Nielsen School. While they could cross at either Peppertree or Amarillo Road on their way to school in the morning, students crossing at Amarillo and proceeding easterly toward Peppertree in the evening would have to ride against traffic. Therefore, the recommended route for bicyclists is different from that for pedestrians: they should be advised not to cross at Amarillo if their destination is north- and east-bound. The four-way STOP recommended for Peppertree Road would benefit bicyclists who cross at that intersection. Speed Survey As mentioned above, the 85th percentile speed in both directions is 36 m.p.h., which is in excess of the posted 25 m.p.h, speed limit. TJKM suggests that consideration be given to changing the speed limit to 30 m.p.h. As outlined in their report, Silvergate Drive is not subjected to "through" traffic, and the raising and lowering of speed limits does not change the speeds at which motorists drive. TJKM indicates that changing the speed limit to 30 m.p.h, would not increase speeds but merely decrease the percentage of motorists who are not in compliance with the speed limit. The Police Chief and City Manager recommend that the speed limit be left at 25 m.p.h, at this time. Betlen Drive Intersection As discussed at the September 22nd meeting, the left-turn pocket was not repainted following slurry seal. This has been pointed out to the City maintenance department and will be corrected, including the arrow mentioned in the TJKM report. The modification of the median mentioned in relation to southbound traffic would require further Staff study in relation to cost and design. Dublin Boulevard Intersection TJKM recommends maintaining the two-way STOP at the present time; however, this intersection will receive further study in relation to the Hansen Ranch Development, and other recommendations may be appropriate in the future. -z- MEMORANDUM 4637 Chabot Drive, Suite 214 Pleasanton Ca. 94566 (415) 463-0611 DATE: October 22, 1986 TO: Lee Thompson FROM: Chris D. Kinzel SUBJECT: Silvergate Drive Study As you know, we have been investigating traffic conditions along Silvergate Drive. At the September 22 City Council meeting, a number of issues were raised by area residents. The purpose of this memo is'to summarize our study and findings of all traffic issues pertaining to Silvergate Drive. Adult Crossing Guard Warrants The traffic volumes on Silvergate Drive were compared with the minimum volumes for adult crossing guard warrants established by the Dublin City Council in 1985. These warrants state that the vehicular traffic volume must exceed 350 vph in each of any two hours during which 40 or more pedestrians are going to or from school. Vehicular Volumes The traffic volumes on Silvergate Drive west of Peppertree Road were counted on September 15-16, 1986 and on September 18-19, 1986. During the a.m. peak hour when children are walking to school, (8:00 ~ 9:00 a.m.) the traffic volume is 401 vehicles per hour. During the afternoon peak hour when children are walking home from the school, (2:00 - 3:00 p.m.) the traffic volume is 297 vph. Therefore, the minimum vehicular volume portion of this warrant is satisfied during the a.m. peak hour and is 85 percent satisfied during the p.m. peak hour. Pedestrian Volumes The number of pedestrians crossing Silvergate was counted on Monday, October 6, 1986, between 8:00 a.m. and 9:30 a.m. The peak hour for pedestrians occurred between 8:00 and 9:00 a.m. The number of pedestrians crossing Silvergate during the peak hour was: at Castilian Road - 4; at Amarillo Road - 14; at Peppertree Road - 28. The total number of pedestrians crossing Silvergate Drive was 46. In addition to these pedestrians, 27 bicyclists crossed Silvergate Drive between 8:00 and 9:00 a.m. The number of pedestrians crossing Silvergate Drive between 1:45 and 3:15 p.m. was counted on Thursday, September 18, 1986, at Amarillo and Peppertree Road. The total number of pedestrians during the peak hour was 24. Since. the number of pedestrians crossing at Castilian Road was not counted, the total number of pedestrians crossing Silvergate Drive is probably higher than 24 during the p.m. PLEASANTON · SACRAMENTO · FRESNO · CONCORD Mr. T'hompson -2- October 22, 1986 peak hour. Therefore, the existing pedestrian volumes satisfy the warrant for adult crossing guards during the a.m. peak hour. During the p.m. peak hour, the warrant is at least 60 percent satisfied, by existing pedestrian volumes. Survey Results One hundred twenty-four surveys were returned as of October 14, 1986. Thirty-six responses indicated that their children currently walked to school. Forty responses indicated that their children would walk if an adult crossing guard were available on Silvergate Drive. Forty-eight responses indicated that their children would be transported to school whether or not an adult crossing guard were available on Silvergate Drive. Of the 40 responses indicating that their children would walk if an adult crossing guard were available, 16 indicated that they had one child, 17 indicated that they had two children and seven indicated that they had three or more children. Therefore, at least 40 and potentially 71 children are represented by this response. It is our conclusion that the pedestrian volume during the afternoon peak hour would satisfy the warrant's requirement of at least 40 pedestrians if an adult crossing guard were present. Although the afternoon vehicular volume does not currently meet the warrant's requirement of 350 vph, the traffic volumes on Silvergate Drive are expected to increase due to the construction of new homes west of Silvergate Drive. Recommendation Therefore, it is recommended that an adult crossing guard be placed at the intersection of Silvergate Drive and Amarillo Road. During the a.m. peak hour, this location currently meets the warrant's minimum vehicular volumes and would meet the warrant's minimum pedestrian volumes if all pedestrians crossed Silvergate Drive at a single location. During the p.m. peak hour, the vehicular volume warrant is 85 percent satisfied and, according to the survey results, the minimum pedestrian volume would be satisfied if an adult crossing guard were present. A cross walk should be painted on the north leg of Peppertree Road at Silvergate Drive to direct children to the adult crossing guard at Amarillo Road. Stop Sign Investigation Minimum Volume As discussed in our letter of September 17, 1986, the total traffic volume entering the intersection of Silvergate Drive and Peppertree Road exceeds the minimum volume warrant of 300 vph for nine hours of the day. The traffic volume on Peppertree Road constitutes 24 percerit of the total traffic entering the intersection. This is less than the warrant specification that 33 percent of the total volume be attributable to the minor street. Mr. ThompsOn -3- October 22, 1986 Accidents In 1984 there was one single-vehicle ~ccident. There were no reported accidents in 1985. To date in 1986, there has been one _vehicle-bicycle collision. This accident involved a southbound vehicle on Peppertree Road and an eastbound bicyclist riding in the westbound bike lane (i.e. the wrong way) on Silvergate Drive. These two accidents within the past three years would not be correctable by four-way STOP signs. Therefore the accident history does not justify four-way STOP signs installation. Collision diagrams of these two accidents are depicted in the attached Figure 1. Visibility The visibility at the intersection was analyzed in light of the results of the speed survey. (The speed survey is discussed on the next page.) The visibility is restricted for northbound vehicles on Peppertree Road looking west. The sight distance as measured from the marked limit line for northbound vehicles on Peppertree Road looking west is approximately 250 feet. The maximum available sight distance of a northbound vehicle pulled forward to the tangent to the curb is 300 feet. The critical approach speed as determined by the speed survey is 36 mph. The minimum design sight distance for a driver on the minor street to cross a major street without requiring traffic approaching at a speed of 36 mph to reduce speed is 360 feet. Although the sight distance would be adequate if traffic were travelling at the posted speed limit of 25 mph, it is less than the design standard for the prevailing speed of 36 mph. Therefore, four-way STOP sign installation would benefit the northbound through and left turn movements on Peppertree Road. Please refer to the following section for additional discussion on this subject. Impact of Adult Crossing Guard on Student Bicyclists In addition to student pedestrians, many students ride their bikes to Nielsen School. This is in part due to the large attendance area for Nielsen School. Twenty-seven bicyclists were counted between 8:00 and 9:00 atm. on October 6, 1986, and 19 bicyclists were counted between 1:45 and 3:15 p.m. on September 18, 1986. Forty of the 46 bicyclists crossed Silvergate Drive at Peppertree Road. Student bicyclists from Peppertree Road could cross Silvergate Drive at Amarillo Road or at Peppertree Road on their way to school during the a.m. peak hour and still be in compliance with traffic regulations pertaining to bicyclists, e.g. riding on the right side of the street with traffic. However, in the afternoon riding home from school, if bicyclists with destinations on Peppertree Road crossed with the adult crossing guard at Amarillo Road, they would then have to ride their bikes eastbound in the westbound bike lane between Amarillo Road and Peppertree Road. This is a concern because riding against traffic either in the bike lane or on the side/valk is unsafe and is a violation of the CVC 21208(a). This was the exact cause of the vehicle-bicycle collision which occurred at this intersection on August 22, 1986. Mr. Thompson -4- October 22, 1986 Therefore, the recommended route to school for bicyclists is' different from that of pedestrians. Although all pedestrians should cross at Amarillo Road with the adult crossing guard, northbound bicyclists on Peppertree Road should cross Silvergate Drive at Peppertree Road. -: " Since the number of school age bicyclists is significant, the intersection of Silvergate Drive and Peppertree Road should be considered on the official route to school for bicyclists. Although there is no official method of intersection control for student bicyclists (like adult crossing guards are for student pedestrians), it is acknowledged that a four-way STOP sign control at Silvergate Drive and Peppertree Road would help the student bicyclists cross Silvergate Drive. Although the survey did not specifically address the potential for student bicyclists, it is likely that they, too, would increase if parents felt more secure about the safety of crossing Silvergate Drive. However, it should be made clear to students and parents that the placement of an adUlt crossing guard to Amarillo Road is not meant to be an endorsement of Amarillo Road as the crossing point for northbound bicyclists on Peppertree Road. We feel the best way to make this clear would be to provide four-way STOP sign control at Silvergate Drive and Peppertree Road. Therefore, it is recommended that STOP signs be installed on Silvergate Drive at Peppertree Road to assist bicyclists and to improve the marginal sight distance problem at the intersection. Speed Survey We conducted a speed survey on Silvergate Drive west of Peppertree Road on Thursday, September 18, 1986. The 85th percentile speed in both the eastbound and westbound direction is 36 mph. This is in excess of the posted speed limit of 25 mph. Continued enforcement will be appropriate on this street. However, it is our observation that Silvergate Drive is unlike many other problem residential streets in Dublin. First, it is not subjected to "through" traffic from outside the area on a regular basis. Secondly, it is a wide thoroughfare designed to comfortably carry the traffic volumes to which it will be subjected. Thirdly, it is our experience that residents who express concerns about speeding are concerned about speeds in excess of 35 to 40 mph. Finally, it has been absolutely demonstrated that raising or lowering speed limits does not raise or lower the speeds that motorists drive, but merely determine what percentage of motorists will not be in compliance with the posted speed limits. Or, in other words, the vast majority of motorists select a reasonable and proper speed to drive based on conditions, regardless of the posted speed limit. Studies have shown that slightly higher, but more reasonable, speed limits may actually lower speeds as they present a more achievable limit for motorists. Therefore, in addition to increase enforcement, we suggest the Council discuss and consider a 30 mph limit on Silvergate Drive. Other Issues Betlen Road/Silvergate Drive At the northbound approach of Silvergate Drive at Betlen Road, there is a striped left-turn lane. A left-turn arrow should be painted in this lane. At the southbound approach of Silvergate Drive, there is a raised median in place of a left-turn lane. Consequently, southbound left turning vehicles must decelerate and turn from the through lane. Given the fact that there is a northbound Mr. Thompson October 22, 1986 left-turn lane, it would make sense to have an opposing left-turn lane for southbound traffic. Although there is sufficient roadway width, it would incur the expense of removing and reinstalling the raised median. We intend to count the number of left turning vehicles at this _intersection during the p.m. peak hour to determine the demand for left turns at the southbound approach. In the absence of this information, we would recommend the relocation of the raised median in order to stripe a southbound left-turn lane. Dublin Boulevard/Silvergate Drive We have reviewed the situation at Dublin Boulevard and Silvergate Drive. The westbound to northbound right turn movement is uncontrolled while all other movements are controlled by STOP signs. We believe this situation merits study. The development of the Hansen Ranch property and the western hill area of Dublin would impact this intersection. This intersection will be studied as part of the Traffic Impact Study of the Hansen Ranch Development which has just started. At the conclusion of this study, recommendations for the Dublin Boulevard/Silvergate Drive intersection will be offered. rah Attachments 157-026M. IMD T LEGEND: (~ RIGHT ANGLE · ~ LEFT TURN ~ REAR-END ~ HEAD-ON SIDE SWIPE, REAR- Et ~ SIDE SWIPE, HEAD-O; PE~D(~BIKE PEDESTRIAN, BICYCLE ~ ~ACKiNG (l) DAYUGHT (D) DARKNESS O PROPERTY DAMAGE Il' FIXED OBJECT (~) INJURY · FATAL El> PARKED CAR ~ OUT .OF CONTROL -. .511_ V££O/~T£ DR. FOF~I CD- 2 JCOLLISION DIAGRAM CiTY OF .Du~ L iN LOCATION PERIOD COVERED: /-/-/994 fo g-3/-/9~ DATE 1 COMPILED: FIGURE 2 WARRANTS FOR FCUR-WAY STOP SIGN INSTAI.LATION Four-way stop si=mn installation may be considered if any of the following conditions exist: (a] Total vehicular volume entering the intersection from all approaches must average 300 per hour for any 8 hours of an average day. (24-hour equivalent approximately 4,000 vehicles.) (b) In addition, the vehicular volume entering the intersection from the minor street or streets for the same 8 hours must average at least 1/3 of the total volume entering the inter- section (100 per hour min.). ACCIDE~YrS Five ore more of types susceptible of correction by stop signs within a 12-month period, with satisfactory observance and en- forcement of less restrictive control. VISIBILITY The straight line sight distance on one or more approaches of the major street for vehicles or pedestrians crossing the inter- section is less than 160 feet. RESIDeNtIAL AREA Volume warrants to be reduced to 60% of the values above if ALL of the follmving conditions are met: (a) Both streets have residential frontage with existing 25 mph speed limits. (b) Neither street is an adopted through street. (c) Neither street exceeds 40 feet of roa~vay width. (d) No existing stop si~n or signal is located on the more heavily traveled street within a distance of 800 feet. (e) Intersection has four legs, with streets extending 800 feet or more mvay from the intersection on at least three sides. (f) Installation of a four-way stop is comparable with overall traffic circulation needs for the residential area. Adult Crossing Guards are normally assign~ where official supervision of elementary school pedestrians is desirable while they cross a public highway on the "Suggested Route to School',. Adult Crossing Guards may Be w-~rrmnted under the following conditions: 1. At uncontrolled crossings: Where there is no alternate crossing guardwithin 1,200 feet; ar~whez~vehiculartraffic volume exceeds 350 vehicles in each of any two daily hours during which 40 or more school pedestrians crosswhile going toor free, school. 2. At STOP sign controlled crossings: Where there is no alternate crossing guard within 1,200 feet; and wherethe vehicular traffic volume on roads of four or more lanes exceeds 500 vehicles per hour during which 40 or more school pedestrians cross going to or from school. 3. At traffic signal controlled crossings: ae Where the numbe~ of vehicular turning movements through the school cros~ exceeds 300 vehicles per hour wh~e school pedestrians are going to or from school. Bo Where there are circumstances not normally present at a signalized intersection, such as crossmzlks more than 80 feet long with no intermediate refuge, or an abnormally high proportion of large c~L"~_rcial vehicles.