Week 6 - Planning for Auto & Intersection Performance/Design Flashcards
What are the factors that fall under planning for the auto?
- components of an auto-based system
- considerations/relationships
- road design
What are the components of an auto-based system under planning for the auto?
a. vehicles: moving objects
b. ways: paths on which vehicles travel
c. facilities: supporting infrastructure
- signals that control auto movements (traffic control devices)
What are considerations and relationships under planning for the auto?
a. Vehicles
- size: influences width of way
- mass: influences material we can use on ways (must be able to support certain weight)
- speed: influences curvature, facilities (traffic control devices)
b. ways classified according to
- function: primary purpose of road (ex. 401 vs king st vs ring rd)
- access: how many points can you enter/exit at?
- speed: what is design/observed speed?
- capacity: max number of vehicles may pass point on roadway over given period of time?
What is road design under planning for the auto?
a. design vehicle
- determines intersection radii
- determines overhead clearance
b. design speed
- determines lane width
- determines vision/sight distance
- related to comfort in horizontal curves
c. curves
- vertical curve (hills/valleys): create sight distance considerations
- horizontal curve: how small/large is curve radius? (can’t have tight turn at high speed for comfort (tilt), safety, visibility)
What are the elements that influence road function?
- speed
- purpose of road
- lane configurations/widths
- volumes
- parking
- presence/volume of pedestrians
- transit
- bikes
- traffic signals
- pavement
What roadway design elements do planner have the most influence over?
- lane widths
- number of lanes
- turning radii at intersections
Why are intersections an important feature in transp networks?
- focus of activity (concentration of travel destinations nearby)
- conflicting movements (various modes crossing each other)
- traffic control (signs/signals control)
- capacity (limited by traffic controls)
What are the key design challenges of intersections?
Goal is to maximize both efficiency and safety of traffic operations within intersection for all users
- always trade-offs in balancing efficiency and safety
- ex. range of vehicles, signage, cognitive ability, walking speeds, operating space for cyclists/transit
What are the levels of service (LOS) for intersections?
A: short delay, most vehicles do not stop b/c they are favoured, short cycle length
B: short delay, many vehicles only stop for short time
C: moderate delay, many vehicles stop, longer cycle lengths
D: longer delays, long cycle lengths, high volume to capacity ratios
E: long delays, long cycle lengths, high volume to capacity ratios
F: delays considered unacceptable to most drivers, capacity unacceptable
What LOS do we typically design for?
- usually design for D level for peak periods
- A would be inefficient the rest of the day (high investment $, greater operating costs, less compatible with other modes, underutilization during day)
What are the benefits/drawbacks of roundabouts
- slows vehicles down as they enter
- reduces conflict/collision points
- doesn’t accommodate pedestrians well
- better vehicle flow
What is intersection analysis?
- need to understand delay
- consider DHV (design hourly volume - total traffic in both directions of travel) to determine which land configurations allow intersection to function for cars & minimizes area necessary
- identify conflict movements (ex. left turns)
- identify phases of movement (signalized intersections)
- collectively, phases combined called the cycle time
What is critical volume?
- for each phase, highest maximum lane volume among the movements for that phase
- green time calculation based on cycle length and volume
What does intersection design entail/why do it?
- determine critical volumes for phases and intersection overall
- establish overall capacity rating for intersection
- make recommendations for design under diff conditions
- factor in type of turn to establish delay (permissive or protected left)
- for permissive left, incorporate influence of vehicles opposing left
What is the intersection analysis process?
- actual vehicle counts
- factor in impedance affect
- determine max lane volume
- return to assign actual vehicle volumes to lane configuration chosen
- determine crit volume for each phase
- sum critical volumes from each phase to determine intersection crit volume
