1 / 32

2 Lane 2 way Rural hwys

2 Lane 2 way Rural hwys. CTC-340. HMWK. CH 16 # 1, 3, 6 use HCS+ software. 2 lane roads. 80% of nations 4,000,000 miles of paved roads are rural 85% of these are 2 lane Only roadway link where traffic in 1 direction has a direct impact on traffic in other direction

derek-finch
Télécharger la présentation

2 Lane 2 way Rural hwys

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 2 Lane 2 way Rural hwys CTC-340

  2. HMWK • CH 16 # 1, 3, 6 use HCS+ software

  3. 2 lane roads • 80% of nations 4,000,000 miles of paved roads are rural • 85% of these are 2 lane • Only roadway link where traffic in 1 direction has a direct impact on traffic in other direction • Wide set of geometric standards and operating conditions • They provide: • mobility - county seat to county seat • access - to land

  4. Highway Classes • Class 1 motorists expect to travel at high speeds – major intercity highways, primary arterials, collectors • Serve mobility needs • Class 2 – access routes, scenic & recreational routes, routes through rugged terrain • Serve access needs • Class 3 - • F 16.1

  5. Highway Classes • Class 3 – serve as main streets – reduced speed limit, no passing, more roadside driveways, and unsignalized junctions • F 16.1

  6. Design Standards • Set by AASHTO standards • Most important design factor = design speed • T16.1 shows recommended design speeds for different facility types • F 16.2 recommended design criteria for max grades

  7. Passing • unique feature • using opposing lane to pass vehicles • directional flows interact • as flow increases in one direction so does the desire to pass • but flow is also increasing in the opposing direction which reduces the opportunities to pass • capacity is based on both directions of travel

  8. Passing • Heavy vehicles have a major impact on roadway capacity • Platoon formation behind slow moving vehicles is common

  9. Passing Sight Distance • Must maintain safe stopping sight distance over entire highway • Passing is an important part of the capacity of a 2 lane road • Must know required passing sight distance • d1 +d2 +d3 +d4 • d1 = Distance traveled during PR time + initial accel to point of encroachment into left lane • d1 = 1.47t1*(S-m+at1/2) • t1 = PR Time (sec); S = speed of passing vehicle (mph); m = difference between spd of passing and passed veh (mph); a = accel of passing veh (mph/s)

  10. Passing Sight Distance • d2 = Distance traveled while passing vehicle is in left lane • d2 = 1.47St2 • t2 = time passing vehicle occupies left lane • d3 = Distance between passing vehicle at end of maneuver and opposing vehicle • d3 = 100 – 300 feet • d4 = Distance traversed by opposing vehicle for 2/3 time the passing vehicle occupies the left lane or 2/3 d2 • d4 = 2/3 d2

  11. Passing Sight Distance • Assumptions • Spd of Passing car is 10mph greater than passed car • Acceleration rate = 1.4 – 1.5 mph/s • PR times = 3.6 – 4.5 s • Time in left lane = 9.3 – 11.3 s – based upon spd parameters • Clearance distance – lower spds use lower range • Minimum values for PSD T 16.2 • Warrant PSD T16.3 – used for posting NO PASSING signs • Want to maximize passing zones

  12. Capacity & LOS • Models based on simulation & limited field study – hard to find 2 lane roads @ capacity • Capacity • Max under base conditions = 3200pc/h total • 1700 pc/h in 1 direction • Base conditions • 12 foot lanes, 6 foot usable shoulder, level terrain, no HV, 100% PSD available, 50/50 traffic split, no traffic interruptions

  13. Capacity Analysis • density is not meaningful since capacity is measured as the total of both directions of travel

  14. Capacity & LOS • LOS • 3 MOE • Average travel speed (ATS) • Average spd of all vehicles traversing the segment for a specified time period (peak 15 minutes) • Can be both directions or 1 depending on analysis • % time spent following (PTSF) • Aggregate time that all drivers spend in queues, unable to pass, with speed restricted by queue leader • % of vehicles following at headways <= 3.0 sec

  15. Capacity & LOS • LOS • Percent FFS – comparison of prevailing speed to FFS • T16.4 - LOS criteria

  16. Capacity & LOS • Class 1 use ATF & PTSF • Class 2 uses only PTSF – not meant for mobility • Class 3 use PFFS • Operational deterioration occurs at a relatively low v/c ratio • Only roadway where this occurs • Leads to improper passing and accidents • Safety issues will demand that road be reconfigured

  17. LOS • LOS deteriorates rapidly at low flows on 2 lane roads • as volumes increase the passing opportunities decrease • F 16.4 • LOS A - D cover 0 - 1600 pcph • LOS E covers 1600 - 3200 pcph

  18. Narrow Lanes and shoulders • look at usable shoulder • on 2 lane roads shoulder functions as storage area for breakdowns, slow vehicle lane to allow queued vehicles to pass • small shoulders have a large impact on capacity

  19. Analysis • 2 types • Single directional analysis of general extended sections in level or rolling terrain (>= 2 mi) • Single direction analysis of specific grades

  20. Analysis • FFS • Should be field info • Representative sample of 100 or more vehicles • Total 2 way traffic flow >= 200pc/h • All vehicle speeds observed or systematic sampling • Sample should mirror analysis type • If Total 2 way traffic flow >= 200pc/h then • FFS = Sm + 0.00776(vf/fHV) • Sm = mean spd of sample, vf = observed flow rate

  21. Analysis • FFS = BFFS – fLS – fA • BFFS can be taken as • (Cl 1 – 55-65mph, Cl 2 – 45 – 50mph, Cl 3 – 40 -50mph) • Design spd • fLS = lane & shoulder width T 16.5 • fA = Access point density T 16.6 • Can be taken as Spd Lmt + 5-7mph

  22. Analysis • Find FFS • 2 lane rural hwy, 10.5’ lanes, 4’shoulders, 20 access points/mi, BFFS = 55mph

  23. Demand Flow Rate • v = V/(PHF*fHV*fG) • 2 conversions based on 2 different sets of adjustments (ATS & PTSF) • need to convert both subject & opposing volumes • Determination of demand flow rates are iterative (only 1 iteration)

  24. Grade adjustment factor • Depends on type of grade • General terrain for ATS & PTSF T16.7 • Specific Upgrades for ATS T16.8 • Specific Upgrades for PTSF T16.9 • Specific downgrades for ATS & PTSF T16.10

  25. HV Factor • fHV = 1/(1+PT(ET-1) + PR(ER-1)) • T16.10 -gen’l terrain & specific downgrades for ATS & PTSF • T16.11 & 16.12 - specific upgrades for ATS • T16.13 - specific upgrades for PTSF • T16.10 – specific downgrades

  26. HV Factor • Truck crawl speed • May need to go down hill slowly to maintain control • fHV = 1/(1+PTC*PT(ETC-1) +(1-PTC)*PT(ET-1)+PR(ER-1)) • T16.14 • PTC = % of trucks at crawl speed

  27. Estimating Average Travel Speed • ATSd = FFS – 0.00776(vd+vo)-fnpA • vd= demand flow rate in direction of analysis • vo= demand flow rate in opposing direction of analysis • fnpA = adjustment to ATS for no passing zones in study area – T 16.15

  28. Determining PTSF • PTSFd = BPTSFd +fnpP(vd/(vd+vo)) • BPTSFd = 100(1-exp(avdb)) • fnpP= adjustment to PTSF for no passing zones in the study area T 16.16 • a,b calibration constants T16.17 • LOS T16.4

  29. Impact of Passing lanes • Passing lanes allow platoon to break up • Can avoid long platoons behind a vehicle • Steps • 1) assume no passing and find ATSd, PTSFd • 2) Find the 4 subsegments of the segment • Lu = subsegment upstream of passing lane • Lpl = subsegment that is the passing lane including tapers • Lde = effective downstream length of the passing lane T14.23 • Ld = subsegment downstream of the effective downstream length of the passing lane • Sum is equal to the total length of the directional segment

  30. Impact of Passing lanes • Lde reflects observations that the passing lane improves the ATS and the PTSF downstream of the passing lane • Effective distance varies depending on demand flow rate and whether ATS or PTSF is involved • Effective distance does not include the passing lane • Ld = L – (Lu +Lpl +Lde) • Lde , Ld will differ for ATS & PTSF

  31. Impact of Climbing Lanes • Added to avoid long queues • Warranted when • Directional flow rate on the upgrade exceeds 200 vph • Directional flow rate for trucks on the upgrade exceeds 20 vph • Any of the following conditions apply • A speed reduction of 10mph for a typical heavy truck • LOS E or F exists on upgrade • LOS on upgrade is 2+ LOS below existing LOS on the approach

  32. Impact of Climbing Lanes • ATS & PTSF values may be modified to take climbing lane into account except that • Ld = Lu = Lde • fpl = are selected from T14.26

More Related