Induced Traffic
Induced traffic is sometimes called induced demand or induced travel.
What is induced traffic and how is it caused?
- Additional traffic caused by people who choose to use their cars when otherwise they would not. In this case, we are most concerned about rush hour traffic.
- During any rush hour, there remain a large number of cars in driveways and garages. Their owners choose not to drive because they have one of the following options:
- they can drive at another time of the day (they don't work at job with strict 9 to 5 style hours),
- they can take public transit,
- they can walk, bike, in-line skate, ...,
- they can car pool,
- they can choose to work from home.
- People choose not to drive in many cases to avoid congestion and the proof is all those cars sitting in driveways and garages during rush hour.
- If you reduce congestion on parts of some roads, some of the people who previously chose not to drive during rush hour may use their cars where they previously didn't. Even very localized congestion relief encourages some people to use their cars.
- The prerequisites for induced traffic are
- roads that have some congestion during rush hour,
- some people who have a choice about driving during the rush hour.
What evidence do we have for induced traffic?
- Transport Canada endorses using tools such as TransDec for planning transportation projects and TransDec accounts for induced traffic (they use the term induced demand).
- The Conference Board of Canada published a briefing paper in December 2006 titled "Build It and Will They Drive? Modelling Light-Duty Vehicle Travel Demand". On page 2 of that report they acknowledge "The consensus in the literature is that for every 1 per cent increase in road network capacity, there is a corresponding increase in the short run of 0.2 to 0.6 per cent in vehicle kilometres traveled. In the long run, this percent increase rises to 0.6 to 1".
- Hard evidence from the City of Ottawa's own traffic counts showing increases well beyond those predicted by forecasts that ignore induced traffic: APETIS report from 1999.
- Induced traffic literature survey by Darin Burleigh.
- Do your own web Google search on "induced traffic, travel, demand" and see how much has been written describing this effect.
Implications for the Alta Vista Corridor:
- The City is not accounting for induced traffic in their predictions. Their predictions have exactly the same number of cars on the road during rush hour for all their alternatives regardless of how much congestion there is and regardless of where that congestion is. This failure to account for induced traffic hides some of the negative impacts of road expansions alternatives such as increased congestion, increased pollution and green house gas emissions.