This is a screen shot from Bay Bridge Explorer, a new iOS app that lets drivers test out an upcoming Bay Bridge detour.

SAN FRANCISCO--Starting this Memorial Day, drivers heading east across the San Francisco-Oakland Bay Bridge will encounter a detour that radically changes patterns developed over many years. But now they have an iPad or iPhone app with which they can practice the new route.

At a briefing today held at the Autodesk Gallery here, the institutions running the construction of the new eastern span of one of the busiest bridges in the world--CalTrans, the Bay Area Toll Authority, and the California Transportation Authority--unveiled Bay Bridge Explorer, an iOS app that lets people "drive" the detour as a way of preparing themselves in advance. That's seen as important since many drivers have developed an expectation of what to expect over many years of driving the bridge, and encountering something new could startle some.

Construction has been going on for years on an entirely new eastern span of the bridge that is up to current seismic codes, something that is crucial in a region that is nearly guaranteed to have a major earthquake in the next 30 years or so and for a bridge that is an essential link between population centers on opposite sides of the San Francisco Bay.

With the new app (see video below, but be patient with the lighting conditions), all iPad and most iPhone and iPod Touch users will be able to get behind the wheel of a virtual car and test out both the existing route and the new detour. The app gives a very realistic view of the eastbound drive--which is the lower level of the bridge--heading into Oakland and showcases a new southward curve at the bottom of the ramp leading to Oakland.

For now, the app will showcase only the new eastbound detour and is available only for iOS devices. But future versions of the app will feature other major detours, and may be available on other mobile platforms, such as Android. The app is part of a larger set of tools the three agencies are making available to Bay Area drivers in a bid to educate them about the major changes coming in advance of the planned 2013 opening of the new eastern span of the bridge.

Other online tools include 360-degree digital visualizations of the bridge and its construction, as well as a Google Earth integration of the work.