Toyota Motor Corp. tentatively is set to release 400 additional electronic data readers in the U.S. in coming months, on top of the 100-150 expected to arrive this month or in April, Ward’s learns.

The readers, which Toyota still considers to be prototypes, will present information gleaned from Toyota’s on-board electronic data recorders in “plain English,” U.S. spokesman Brian Lyons says.

“There is an intermediate step, but the EDR reader handles it all itself,” Lyons says, noting Toyota’s EDR reader converts what is known as hexadecimal data into English.

EDRs can record various vehicle events, such as accelerator pedal position and whether a driver was wearing a seatbelt.

Lyons notes events not recorded by Toyota EDRs, due to differences in the device across model lines, will be transmitted as a “no” on the EDR reader.

The data on the auto maker’s EDRs, or black boxes, up to now has not been accessible to consumers absent an order by a judge or the National Highway Traffic Safety Admin.

Toyota currently has just one in-house prototype tool in the U.S. to read its EDRs.

In September 2012, beginning with ’13 vehicles, NHTSA will require auto makers whose vehicles have EDRs to record a specific set of events at certain time intervals. NHTSA also is mandating the data be accessible to consumers via a commercially available reader tool.

Lyons says Toyota plans to comply with the law early, although he cannot say when the tool will be commercially available.

Last week, Lyons said Toyota’s EDR readers likely will be kept at its U.S. regional sales offices, not by dealers.

Separately, Lyons says Toyota is investigating Monday’s incident of a runaway Prius hybrid-electric vehicle in San Diego.

While driving on a freeway yesterday afternoon, Jim Sikes dialed 911 after his ’08 Prius allegedly accelerated unintentionally.

A California Highway Patrol officer responded, telling Sikes by loudspeaker to depress the Prius’ brake pedal and also apply the electronic brake to stop the vehicle.

Brian Jennings, information officer for the California Highway Patrol’s El Cajon office, tells Ward’s Sikes says he did not attempt to put the car in neutral, nor did the responding officer suggest he take that action.

“The officer had a mental checklist in his mind of what he wanted to do,” Jennings says, noting it is up to each officer to decide how to handle complaints of unintended acceleration.

The car was released this morning to Sikes and will be towed to a Toyota dealer for inspection.