Most Public Works Forecasts Off By 100%

A new academic article shows that rail passenger forecasts are regularly overestimated by a staggering average of 106%.

2 minute read

April 13, 2005, 11:00 AM PDT

By Chris Steins @planetizen


" 'How (In)accurate Are Demand Forecasts in Public Works Projects?' examines 183 road and 27 rail projects in 14 countries on five continents, including in the U.S. It found that rail passenger forecasts were overestimated by 106 percent on average, resulting in an actual ridership of less than half of that predicted. For 9 of 10 rail projects, estimates were high, according to the study. One project in eight overshot estimates by more than 400 percent. The study also noted that forecasts are no more accurate now than they were 10, 20, and 30 years ago.

...'My team and I were shocked by our findings. For professional forecasters to be wrong by more than 100 percent and to make no improvement for decades is unheard of. Simple forecasting errors cannot explain this,' Flyvbjerg said. 'By routinely overestimating benefits and underestimating costs, promoters make their projects look good on paper, which helps get them approved and built. The only ones to pay are the taxpayers.' "

The study also covers road investments. For road projects studied, half of all traffic forecasts were found to be wrong by more than 20 percent. This is better than for rail forecasts. But for roads, too, there has been no improvement in the accuracy of forecasts for 30 years, despite millions of dollars spent on improving forecasting models.

From the journal article abstract: This article presents results from the firststatistically significant study of trafficforecasts in transportation infrastructureprojects. The sample used is the largestof its kind, covering 210 projects in 14nations worth U.S.$59 billion. The studyshows with very high statistical signifi-cance that forecasters generally do a poorjob of estimating the demand for transportationinfrastructure projects. For 9out of 10 rail projects, passenger forecastsare overestimated; the average overestimationis 106%. For half of all road projects,the difference between actual and forecastedtraffic is more than ±20%. Theresult is substantial financial risks, whichare typically ignored or downplayed byplanners and decision makers to the detrimentof social and economic welfare.Our data also show that forecasts have notbecome more accurate over the 30-yearperiod studied, despite claims to the contraryby forecasters. The causes of inaccuracyin forecasts are different for rail androad projects, with political causes playinga larger role for rail than for road. Thecure is transparency, accountability, andnew forecasting methods. The challengeis to change the governance structuresfor forecasting and project development.Our article shows how planners may helpachieve this.

[Editor's note: The link below is to a 750KB PDF document.]

Thanks to Chris Steins

Tuesday, April 12, 2005 in Journal Of The American Planning Association

portrait of professional woman

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching. Mary G., Urban Planner

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

Use Code 25for25 at checkout for 25% off an annual plan!

Logo for Planetizen Federal Action Tracker with black and white image of U.S. Capitol with water ripple overlay.

Planetizen Federal Action Tracker

A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

May 7, 2025 - Diana Ionescu

Person in yellow safety suit and white helmet kneels to examine water samples outdoors on a lake shore.

USGS Water Science Centers Targeted for Closure

If their work is suspended, states could lose a valuable resource for monitoring, understanding, and managing water resources.

May 1, 2025 - Inside Climate News

Wide suburban road with landscaped median and light pole banners advertising local amphitheater.

End Human Sacrifices to the Demanding Gods of Automobile Dependency and Sprawl

The U.S. has much higher traffic fatality rates than peer countries due to automobile dependency and sprawl. Better planning can reduce these human sacrifices.

April 29, 2025 - Todd Litman

Large group of people and children on bikes in street.

Unleashing the Power of Cycling With Smart Messaging

Lloyd Alter describes how creative design and copywriting can flip the script and promote active transport.

30 minutes ago - Carbon Upfront!

Wasco Viaduct under construction in California's Central Valley as part of California High-Speed Rail project.

Trump: Federal Government Won’t Pay for California HSR

The President has targeted federal funding for the California bullet train project since his first administration.

May 8 - The Fresno Bee

Bird's eye view of Salesforce Park in San Francisco, CA.

San Francisco Enhances Urban Planning Initiatives with Green Infrastructure

San Francisco incorporates green infrastructure in its city development initiatives, elevating the importance of sustainability in urban planning.

May 8 - The Daily Californian

Urban Design for Planners 1: Software Tools

This six-course series explores essential urban design concepts using open source software and equips planners with the tools they need to participate fully in the urban design process.

Planning for Universal Design

Learn the tools for implementing Universal Design in planning regulations.

Comprehensive Bikeway Design Workshop

Transportation Research & Education Center (TREC) at Portland State University

Early Bird Deadline – save on your tuition fee!🚨

Institute for Housing and Urban Development Studies (IHS)