SIDRA for Environmental Analysis

Aerial photograph of road

SIDRA INTERSECTION and SIDRA TRIP for Environmental Assessments

Environmental assessment in traffic management, design, operations and planning can be conducted using models to estimate fuel consumption and pollutant emissions as a function of traffic conditions. For this purpose, the SIDRA INTERSECTION and SIDRA TRIP software packages use unique models based on work that won the Institute of Transportation Engineers 1986 Transportation Energy Conservation Award for research into energy savings from urban traffic management.

These power-based vehicle energy and emission models combined with a powerful lane-based traffic model enable transportation planners and engineers to carry out environmental analysis for assessing intersection and network traffic solutions. These detailed models incorporated in easy-to-use software packages can be valuable for professionals interested in realistic assessment of the effects of transport on the environment.

These models are documented extensively. This includes more recent research to calibrate the light and heavy vehicle parameters used in the models based on a large empirical database for a modern vehicle fleet. The papers and reports and available for download from the Publications section of our website.

Click on any of the following keywords to view search results from our Publications section.

Fuel
Emissions
CO2
Pollutant
Acceleration

Accuracy of the SIDRA instantaneous CO2 Emission model for a test car

CUEDC-P drive cycle used in SIDRA fuel consumption and emission tests

Graph of SIDRA instantaneous CO2 emission model estimates vs measured CO2 emissions
shows very high correlation

About the Models

Two essential elements of effective fuel consumption and emission modelling in relation to traffic management, design, operations and planning are:

  • A detailed traffic model that has sensitivity to traffic characteristics (road geometry, road grade, traffic control type, demand volumes, driver behaviour, acceleration - deceleration and other vehicle characteristics), and
  • fuel consumption and emission models that have the right sensitivities to vehicle parameters (fuel consumption and emission parameters sensitive to variations in traffic condition, mass, power, acceleration - deceleration characteristics, and so on) and at the same time are well integrated with the traffic model.

SIDRA INTERSECTION and SIDRA TRIP use different levels of model detail but both models are based on the same power-based model of vehicle fuel consumption and emissions.

SIDRA INTERSECTION is a micro-analytical software that uses a four-mode elemental (modal) model of fuel consumption and emissions. For each lane of traffic, it models vehicle paths (drive cycles) consisting of a series of cruise, acceleration, deceleration and idling (stopped) time elements determined for specific traffic conditions represented by intersection geometry, traffic control and demand volumes.

SIDRA TRIP is a single-trip microsimulation model for assessment of road traffic conditions using real-life traffic vehicle travel data (e.g. from GPS data) or user-defined drive cycles. It employs an instantaneous model to determine various trip characteristics for assessing traffic and travel level of service, performance (delay, speed, travel time), and provide estimates of fuel consumption, emissions, noise, operating cost and user cost.

SIDRA INTERSECTION Model for Fuel Consumption Emissions

The vehicle paths (drive cycles) generated by SIDRA INTERSECTION using the four-mode elemental model are very different for different intersection types (signalised, roundabout, sign-controlled), for different signal phasing and signal timing arrangements, and for different congestion levels.

Fuel consumption and emissions are calculated by movement class as applicable to Light Vehicles, Heavy Vehicles, Buses, Large Trucks and up to six user-defined classes.

Vehicle paths (drive cycles) are defined by the initial and final speeds in each element of the driving manoeuvre. Approach and exit cruise speeds, intersection negotiation speeds, queue move-up speeds and acceleration and deceleration times and distances estimated using a polynomial acceleration model are used to determine vehicle paths. The fuel consumption and emission models are applied to queued and unqueued vehicles in each lane separately, and then the total values are calculated for all traffic using the lane. The lane-by-lane results are then aggregated to approaches, intersections, routes and networks.

Vehicle paths for unqueued vehicles are constructed accounting for (i) cruise on entry to the approach road, (ii) slow-down to a safe negotiation speed or full stop on the approach to the intersection, (iii) negotiation of the intersection departure area at the safe negotiation speed, (iv) acceleration to the exit cruise speed and (v) cruise on the exit road.

Vehicle paths for queued vehicles account for (i) cruise on entry to the approach road, (ii) major stop or slow down from approach cruise speed, (iii) queue move-ups (repeated stops and starts in the queue), (iv) negotiation of the intersection departure area at the safe negotiation speed, (iv) acceleration to the exit cruise speed and (v) cruise on the exit road.

Once the vehicle travel paths are determined, the fuel consumption and emission values are calculated for each of the four driving elements (modes) for each vehicle path, the results are added together for the entire vehicle path, and aggregate values for movement classes, lanes and approach (turning) movements are determined according to flow proportions of queued and unqueued vehicles.

This model provides highly accurate fuel consumption and CO2 emission estimates for traffic analysis unlike models that simplify traffic information into such aggregate variables as average travel speed or delay and number of stops (three-mode elemental model).

The key to the estimation of fuel consumption and emissions in SIDRA INTERSECTION software is detailed modelling of stop-starts in addition to delays and queues. Accelerations involved in stop-starts are a major cause of fuel consumption and emissions. Readers may be interested to know that stop-start modelling is not included in the US Highway Capacity Manual. SIDRA INTERSECTION software includes consistent modelling of stop-start behaviour of vehicles at intersections of different types including a unique gap-acceptance model by signal analogy as a basis of modelling stop-starts for roundabouts and intersections controlled by stop and give-way (yield) signs.

SIDRA Four-Mode Elemental Model applied to a vehicle path (drive cycle) for a simple stop-start manoeuvre

SIDRA Four-Mode Elemental Model
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