Are Cost Estimators Bad at Their Jobs?

San Francisco's Transbay Transit Center is just the latest example of an urban mega-project experiencing an enormous cost overrun. Eric Jaffe examines what the causes of this all too common phenomenon might be.

1 minute read

July 30, 2013, 1:00 PM PDT

By Jonathan Nettler @nettsj


"So how did it get to the point where the only thing we can confidently expect from a big infrastructure project is that it will cost way more than expected?"

"One thing's for sure: the people who predict the cost of urban mega-projects do a terrible job," writes Jaffe. "Several years ago the University of Oxford scholar Bent Flyvbjerg, who's made a career researching mega-project mismanagement, analyzed 258 transportation infrastructure projects from around the world and found that nine in ten exceeded their cost estimates. The overruns were greater on rail projects than road projects but averaged 28 percent across the board."

"Whatever the underlying causes of cost overruns may be, there seems to be one promising means of addressing them: creating a 'reference class' of similar projects to serve as a platform for comparing costs. The idea, as explained by [psychologist Daniel] Kahneman in 2003 [PDF], is that old outcomes can serve as a barometer for recognizing just how unrealistic a biased new prediction might be — and help adjust it accordingly. Such a strategy controls for both political chicanery and cognitive biases alike."

Tuesday, July 30, 2013 in The Atlantic Cities

courses user

As someone new to the planning field, Planetizen has been the perfect host guiding me into planning and our complex modern challenges. Corey D, Transportation Planner

As someone new to the planning field, Planetizen has been the perfect host guiding me into planning and our complex modern challenges.

Corey D, Transportation Planner

Ready to give your planning career a boost?

Broken, uneven sidewalk being damaged by large tree roots in Los Angeles, California.

The City of Broken Sidewalks

Can Los Angeles fix 4,000 miles of broken sidewalks before the city hosts the 2028 Olympic Games?

December 5, 2024 - Donald Shoup

Large store in mall with yellow and black STORE CLOSING sign on front.

Shifts in Shopping: Transforming Malls Into Parks

Maybe zombie malls still have a second life — one with a little greenery.

December 8, 2024 - Ruscena Wiederholt

Multifamily housing under construction.

To Build More Housing, Cities Must Be Smarter in How They Use Land

How strategic land use policy decisions can alleviate the housing crisis and limit unsustainable sprawl.

December 11, 2024 - John D. Landis

View of brick buildings and One World Trade Center building and New York City skyline.

NYC’s Proposed Zoning Reforms Lag Behind Other Cities

Cities like Austin and Minneapolis are making major changes to their zoning codes to encourage housing construction, but New York’s proposed reforms are far less ambitious.

6 seconds ago - The City

Heavy traffic on freeway in San Diego, California.

Why Traffic Never Gets Better

Despite abundant research showing that roadway expansions provide limited congestion relief and increase long-term traffic problems, they still occur due to wishful thinking: advocates claim that “this” project is different.

December 12 - Greater Greater Washington

Trolley bus in San Francisco, California.

San Francisco Tops ‘Urban Mobility Readiness’ List

An annual analysis of global cities assesses public transit, technology, and sustainability.

December 12 - Bloomberg CityLab

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.