Enhanced signalling
Transport agencies have long relied on signals, including traffic lights, ramp meters and roadside displays, to manage traffic flow. A range of advanced signalling solutions can help policymakers to improve the sustainability of transport systems. More specifically, signalling can improve the efficiency and convenience of sustainable transport modes like public transport and active modes compared to private motorised vehicles. For example, signalling can reduce the need to break and accelerate for public buses or cyclists, shortening travel times and reducing energy use. Shifts to more sustainable modes may be achieved as a result.
On the other hand, signalling can also make driving private motorised vehicles more efficient, reducing energy use and related emissions. Policy makers should consider potential rebound effects; more efficient vehicle operations may increase demand or non-desired mode shifts. Demand management measures can mitigate unwanted indirect effects and ensure that signalling measures lead to overall emissions reductions.
Advanced signalling solutions include:
- Signal Synchronisation; traffic signals along a corridor are synchronised to create a “green wave” of efficient traffic flow.
- Adaptive Signal Control; signals are adjusted automatically or from a control centre in response to current traffic conditions.
- Signal Priority; signals detect approaching high-priority vehicles, like buses, and prioritise access.
- Signal Phase and Timing (SPaT) Broadcasting; roadside units send information to vehicles that can adjust their speed to minimise idling and acceleration. [This measure is evaluated under ITS - Smooth Driving.]
Smooth driving measures can improve energy efficiency and reduce a vehicle’s tailpipe and upstream CO2 emissions per vehicle kilometer driven. The size of energy efficiency gains will depend on the general energy efficiency of the vehicles. Gains will therefore change over time with the uptake of low- or zero-emission vehicles (LZEVs).
Empirical studies estimate carbon emissions reductions of up to 10% with advanced signalling for motorised vehicles near signal controls. For example:
- Signal Synchronisation
- 5% (Pandazis, 2015)
- 7% (ITS International, 2011)
- Adaptive Signal Control
- 5% over static optimisation (AERIS, 2016)
- 2% (Klunder, 2009)
- 18-19% with connected vehicles (Zhang, 2018; Yang, 2018)
- Signal Priority
- 3% for transit (AERIS, 2016)
- 1-2% for transit (Barth, 2015)
These assessments do not take any indirect effects into account. These may be positive due to more sustainable mode shifts, or negative where travel efficiency improvements lead to undesired mode shifts or induced travel.
Actual costs from implementations in the United States are available for each advanced signal technology.
- Static Signal Optimisation
- USD 5 800 per corridor-km including operations and maintenance (O&M) discounted at 4% (Lodes, 2013)
- USD 2 500 - 3 100 per signal (USDOT, 2007)
- Signal Synchronisation
- USD 4 200 per signal (MTC, 2016)
- Adaptive Signal Control
- USD 24 000 per intersection (Frost, 2017)
- USD 55 000 per intersection + USD 500 000 for communication network (Hook, 2014)
- O&M costs USD 750 per intersection (Hook, 2014)
- USD 28 800 per intersection, USD 18 000 per corridor-km including O&M discounted at 4% (Lodes, 2013)
- Video-based systems are about twice as expensive (Lodes, 2013)
- Signal Priority
- USD 2 500 - 40 000 per intersection and USD 50 - 2 500 per vehicle (Danaher, 2010)
Advanced traffic signals can reduce average travel times where rebound effects of increased travel activity of the targeted mode can be avoided.
- Traffic signals favouring private motorised vehicles can increase their use and discourage the use of less polluting modes.
- Signal priority for public transport, cyclists and pedestrians may increase emissions for other traffic. Although these emissions may be offset by increased uptake of more sustainable modes, it is important to consider them.
- Ramp Metering, which limits traffic entering a motorway to prevent congestion, causes stop-and-go traffic and waiting times on ramps. As a result, travellers may choose less efficient alternative routes, where congestion may occur.
ITF (2021) Transport Climate Action Directory – Enhanced signalling
https://www.itf-oecd.org/policy/enhanced-signalling
AERIS (2016) Applications for the Environment: Real-Time Information Synthesis (AERIS) Capstone Report: 2009 to 2014 Executive Summary, https://www.its.dot.gov/research_archives/aeris/pdf/AERIS_Capstone_ExecSummary.pdf
Barth M.J., Wu G., Boriboonsomsin K. (2015) Intelligent Transportation Systems and Greenhouse Gas Reductions, https://link.springer.com/article/10.1007/s40518-015-0032-y
Danaher A. R. et al. (2010) TCRP Synthesis 83: Bus and Rail Transit Preferential Treatments in Mixed Traffic, http://onlinepubs.trb.org/onlinepubs/tcrp/tcrp_syn_83.pdf
Elkins S. and Niehus G. (2012) InSync Adaptive Traffic Control System for the Veterans Memorial Hwy Corridor on Long Island, NY, http://www.dot.ny.gov/divisions/engineering/technical-services/trans-r-and-d-repository/C-10-01%20Final%20Report%20August%202012.pdf
Frost A. (2017) Iteris awarded traffic management and communications upgrade project in Texas, https://www.itscosts.its.dot.gov/its/benecost.nsf/ID/FFCA8E00F7022A14852582130059C34E?OpenDocument&Query=Home
Hook J. (2014) Improving stop-and-go traffic would cost Chambersburg $34,000 a year, https://www.itscosts.its.dot.gov/its/benecost.nsf/ID/C37617999914FC8385257DCC00575573?OpenDocument&Query=Home
ICF (2013) Programming for Operations: MPO Examples of Prioritising and Funding Transportation System Management & Operations Strategies, https://ops.fhwa.dot.gov/publications/fhwahop13050/fhwahop13050.pdf
ITS International (2011) Benefits of Traffic Light Synchronization, https://www.itsbenefits.its.dot.gov/its/benecost.nsf/ID/9F9C493D6F9126DF852578150071F98F?OpenDocument&Query=Home
Klunder G. A. (2009) Impact of Information and Communication Technologies on Energy Efficiency in Road Transport: Final Report, https://www.narcis.nl/publication/RecordID/oai:tudelft.nl:uuid:2a2c6c59-0ddd-4a93-91b2-0ca7d363918c
Lodes M. and Benekohal R. F. (2013) Safety Benefits of Implementing Adaptive Signal Control Technology: Survey Results, http://hdl.handle.net/2142/45786
Metropolitan Transportation Commission (MTC) (2016) Program for Arterial System Synchronization (PASS) FY 14/15 Cycle - Fact Sheets, http://mtc.ca.gov/sites/default/files/PASS%20Fact%20Sheets%2014-15%20ALL.pdf
Pandazis J.-C. and Winder A. (2015) Study of Intelligent Transport Systems for reducing CO2 emissions for passenger cars, https://erticonetwork.com/wp-content/uploads/2015/09/ITS4rCO2-Report-Final-2015-09-10-submitted.pdf
Shaheen S. and Finson R. (2013) Intelligent Transportation Systems, https://escholarship.org/uc/item/3hh2t4f9
US Department of Transport (2007) Intelligent transportation systems for traffic signal control: deployment benefits and lessons learned, https://rosap.ntl.bts.gov/view/dot/2352
Weikl S., Bogenberger K. and Bertini R. L. (2013) Empirical Assessment of Traffic Management Effects of a Variable Speed Limit System on a German Autobahn: Before and After, https://trid.trb.org/view/1241566
Yang H., Haque M. and Wu X. (2018) Connected Vehicle-Enabled Proactive Signal Control for Congestion Mitigation on Arterial Corridors, https://trid.trb.org/view/1495834
Zhang L. et al. (2018) Benefits of Early Deployment of Connected Vehicles at Signalized Intersections, https://trid.trb.org/view/1496486
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