Traffic Engineering - Statistics

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Answer Stats

Hint	Answer	% Correct
Regression to mean#	Random fluctuations in crash number periods with high number may be followed by numbers for the same area This is because of the regression t mean phenomenon. results in over-estimations of the effectiveness of an intervention intented to imrpive safety; so needs to be looked at for many years for consistency\	100%
Alternative Strategies for network junction control#	1. Fixed time control during time periods when overloaded conditions are expected + Vehicle Actuated at other times. 2. Measure traffic characteristics across the network and compute optimal combination of cycle time, Phase/stage split and offsets to either minimise network delay or maximise network capacity, + allow local optimisation of intersection control (early termination, skip phases). 3. As above but use a forecasting model to anticipate traffic and hence optimum settings\	0%
Crossing design#	Account for 'desire paths' where ped would walk if unrestrained Have a clearance period after green\	0%
Conflict#	A conflict between two or more phases exists if these cannot receive green at the same time\	0%
Phase#	A set of streams that receive identical signal indications at the same time\	0%
Dynamic Hard shoulder operations#	before opening hard shoulder check with cctv to make sure it is all clear and signal accordingly image\	0%
Limitations of ramp metering#	Congestion problems causes by a downstream bottleneck reduction of road capacity because less lanes available traffic queueing back from an off slip and blocking a lane on the main carriageway roadworks/ accident resulting in closure of lanes\	0%
SCOOT traffic model#	Constructs a smoother traffic cyclic profile flow for each link Stop line arrival profile made by offsetting cyclic flow profile by the link journey time Flowchart\	0%
Improvements to smart motorways#	Convert dynamic hard shoulder sections to all-lane running Improve spacing of emergency areas more communication with drivers improving public information displaying emergency areas on stanavs updating highway code for more guidance\	0%
Cyclist measures#	Cycle lanes with separate barriers Signs and routes Toucan and Soarrow crossings\	0%
Fixed time signal variables#	Degree of saturation - measure of efficiency should be < 1 Cycle time - Influenced by a series of constraints Effective green time\	0%
Smart motorway operations#	designated emergency areas built Maintenance issues mitigation against hazards caused by incedents time to repair\	0%
Factors affecting saturation flow#	Direction of traffic external factors - lane width, turning radius, slop\	0%
Car following#	Driver behaviour combined with vehicle characteristic leads to variations in speed, deceleration and acceleration rection times can lead to excessive braking, forming shockwaves and traffic growth\	0%
Clearance time#	Ensures that two incompatible stream that have green successively dont collide creates time gap between end of green phase and start of green for the next phase\	0%
Effective green time#	Equivalent time of discharge of a queue with a constant departure rate (saturation flow)\	0%
Speed studies#	Establish parameters for traffic operation and control evaluate the effectiveness of traffic control devices speed vs safety\	0%
Speed limits#	Evidence led and self explaining to reinforce peoples assessment of what is a safe speed to travel key source of information to road users; indicate the nature of risks for themselves and others on the road\	0%
Collision classification#	Fatal Serious injury slight injury damage only\	0%
Time to repair - Smart motorways#	Fault triage - what is wrong Site access - get to the problem location Fault repair and recomission - get technology working Traige tech that self-tests and reports errors remote access via comms network to investigate prioritise faults - not all reported faults prevent operation Access control of roadspace - need for temp traffic management night time working impact on other planned work time to repair must be short enough to minimise risk of a hazard that cannot be fully mitigated\	0%
Signal control strategies#	Fixed time (offline) Online - program reacts to changing traffic conditions: Vehicle actuated - detection of vehicles at stop line (MOVA) Dynamically controlled - signal times determined centrally based on date, time, traffic flow, density speed e.g SCOOT\	0%
Coordination of junctions#	Green wave if green times are synchronised for successive junctions most heavily used junction will have the longest cycle time so this is used as teh common cycle time for the network\	0%
Selecting speed limits#	History of collisions road geometry and engineering road function composition of road users existing traffic speeds road environment\	0%
HIOCC Algorithm - Queue protection#	If detector is detecting for >2seconds send signal for reduced speed limit slow long vehicles can trigger false alarms\	0%
Ratio of inflow to outflow#	If inflow is > outflow queue forms junction needs to be changed if this is the case e.g extra lane\	0%
MOVA delay minimisation#	If no links are over saturated then abs min green time\	0%
Ramp metering process#	image/flowchart\	0%
Incident Management#	Incedent detection and verification initial response and access scene management network restoration\	0%
Fatal Collision#	Individual dead afet certain number of days after collision\	0%
Lane#	Individual line of traffic containing one or more movements\	0%
Congestion Management#	Lower vehicle speeds reduce lane changing reduce variability in headway more stable 'laminar' flow\	0%
Saturation flow, S#	Max rate of departures across a stop line for an individual stream\	0%
Motorway features#	multiple lanes in each direction separated by central barrier minimum radii curves - reduce lateral force and maximise sight lines maximum gradients grade separated interchanges as far as possible no frontage access emergency stopping lanes no ped, slow moving vehicles, animals\	0%
Junction Layout#	Must be safe, efficient and fair\	0%
Road safety statistics#	Number - abs value to give idea of overall scale Normalised by population - per 1mil Normalised by number of vehicles per 1mil Normalised by distance travelled per billion vehicle kilometres\	0%
Phase allocation#	Number of phases to be kept as small as possibles if there are large no. phases then alternative measures to be considered, e.g ban right turn phases grouped into stages in a signal plan\	0%
Limitations of VA signals#	Only max green times optimised difficult to determine set of maxima appropriate at all times Dominant flow on one arm can result in an inefficient junction as delays on other arms may be excessive\	0%
Dynamic control in networks#	Optimum for network is not the same as optimum for individual junction Actual pattern varies from survey need for regular survey and update to keep timings relevant traffic leaving upstream junction may get red at next junction so network is inefficient\	0%
Signing and Lining#	Primary method for highway authorities to convey regulations, instructions and guidance Major maintenance task Major contribution to road safety\	0%
Safe System Principles#	Problem - Manage energy in crashes preventing fata and serious casualties Goal - Zero fatal and severe injuries Planning approaches - Proactively target and treat risk; systematic approach to build a safe road system Causes of the problem - People make mistakes Ultimate responsibility - Shared responsibility by individuals with system designers How it works - Multiple element of a Safe System combine so that if one part fails others can provide protection\	0%
Temporary traffic management design principles#	provision of clear and early warning of obstructions in the highway; optimisation of road space and the provision of an adequate safety zone and working space at works locations; clear directions relating to decisions/actions required from road users; minimisation of potential conflict between road users, and between road users and road workers and their operations; credibility of traffic signs and temporary requirements; and speed limits and restrictions appropriate for the temporary highway geometry and safety features. to maximise the safety of the workforce and the travelling public.\	0%
Queue protection and congestion management#	Queue protection: Hazard, risk and mitigation e.g hazard - collision from driving into rear of queueing traffic risk - likelihood increases as increasing traffic volumes leads to queues forming mitigation - increase driver awareness, lower vehicle speed\	0%
Stopped vehicle detection#	Radar identifies objects that slow down/stop and alerts are sent to the control room cctv personnel verify presence of stopped vehicle and set signals to close lanes, reduce speed and dispatch recovery teams\	0%
Motorway Management Systems#	Ramp metering Queue protection and congestion management Dynamic hard shoulder operations Smart motorways\	0%
Ramp Metering#	Regulates flow from slip road onto main carriageway at level that maximises through put on main carriageway Flow breakdown becomes likely as traffic density slowly builds up at the merge if critical capacity is exceeded flow breaks down\	0%
Pedestrial corssings at junctions#	Require separate phase Full green synchronised crossing period or movement can be with traffic\	0%
Speed study methods#	Road detectors radar based inductive loops cameras\	0%
Signal control objectives#	Safety efficiency management - prioritise certain vehicles e.g busses, trams policy - e.g provide more space for pedestrians and cyclists\	0%
Temporary traffic management#	safety zones and necessary working space number and width of temporary traffic lanes; hard shoulder use? contraflow temp speed restrictions arrangements for access to site\	0%
Low traffic neighbourhood#	Scheme where motor vehicle traffic in residential streets are reduced traffic routed elsewhere\	0%
Dynamic Network control systems#	SCOOT - Split Cycle Offset Optimisation Timing SCATS - Sydney Coordinated Adaptive Traffic System\	0%
Congestion management algorithm#	Set signals to show variable speed limits based on traffic congestion Measure flow and speed at HIOCC detection sites Change accordingly\	0%
SCOOT concepts#	short term prediction of flows fast responce incremental changes dynamic signal timings online traffic model\	0%
Side - fire - radar#	Single device covers multiple lanes, monitors traffic flow in each can be blocked by taller vehicles\	0%
Stream#	Smallest set of movements that form a single queue comprising of one or more lanes\	0%
SCOOT#	Split - green time split cycle - traffic signal cycle time offset - linking of traffic between signals optimisation technique\	0%
SCOOT optimisers#	Split - optimising node green time split between each signal stage Offset - optimising linking between nodes Cycle - Minimising network traffic delay\	0%
MOVA set up data#	The grouping of individual traffic lanes into “links” that have a common movement, e.g. straight ahead, ahead and left, right turn only. • Distances from each detector to the stop-line • Saturation flow information • Typical cruise speed of traffic = 15th percentile speed of vehicles on the approach after the initial queue has finished discharging. • Lane weighting- factors: to allow higher priority to be given to clearing the queue in some lanes when the junction is operating in oversaturated mode. For each link, • the signal stage(s) during which the link receives green, • minimum green time, • whether it is a traffic or pedestrian link • stop penalty ( converts “stop” to a delay in seconds)\	0%
Stage#	The period during which signals are not changing and a set of phases have green\	0%
Movement#	The trip executed between an origin and a destination within a junction\	0%
Smart motorways - All Lanes#	Through junction running - Extending the dynamic use of hard shouldet through the junction Controlled all lane running - converting the hard shoulder permanently to a running lane with speed control access across all lanes\	0%
Issues with dynamic hard shoulder#	Time taken and resources used to open and close hard shoulder cost of maintenance of technology infrastructure capital cost of physical infranstructure design issues around junctions and viaducts\	0%
MOVA Modes#	Under saturated: queue clears in every lane cycle, MOVA minimises delay MOVA compares the benefits (reduction in delay and number of stops on current stage) of extending the green on the current stage against the disbenefit (increased delay on other stages). If benefits exceed the disbenefits then extend green otherwise change to next stage. Maximum green tim Over saturated: Queue in any lane of link doesnt clear MOVA determines oversaturation as occuring when Estimated queue of vehicles exceeds preset value If the IN vehicle detected has been detecting continuously for longer than a preset value MOVA will seek to maximise capacity\	0%
Vehicle actuation between limits#	Use survey data to identify maximum flows design signal plan determine min green times and inter green periods apply optimisation calculations to determine max cycle time and green time no traffic means junction runs at min green times at high flows junction operates at optimised max green times detection system installed to control timings between periods\	0%
Speed management measures#	Visual clues chicanes speed humps technology and psychology\	0%
Microporcessor Optimised Vehicle Actuation (MOVA)#	Well suited for High traffic flow sites experiencing capacity difficulties under VA control with congestion on one or more approaches sites with high speed approches and/or red compliance problems where additional capacity is required to allow ped facilities or safer staging structure Benefits from MOVA 13% delay saving compared to VA 2-3% capacity improvement\	0%
Pedestrian crossings#	Zebra - ped right of way, no signal control Pelican - finds gap in traffic and provides res, otherwise wait until max green time Puffin - checks peds are still waiting after button is pressed, monitors crossing as well\	0%

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