Court records from the San Bernardino terrorist attack released last week shed light on a “nightmare” scenario that was plotted and abandoned by Syed Rizwan Farook and his childhood friend Enrique Marquez: namely, to launch a terrorist attack on the often-clogged 91 Freeway using guns and pipe bombs to murder innocent civilians.

“Transportation targets are fairly common with terrorists, but they usually involve mass transit, aircraft or bridges,” Brian Levin, a Cal State San Bernardino professor and director of Center for the Study of Hate and Extremism, told the Los Angeles Times. “A horrendous operation such as the one envisioned in the complaint not only confines civilians while they would be under vicious attack but obstructs and places first responders at risk from sniper fire as well.”

Although officials reportedly said this was the first alleged terrorist plot involving freeways they’ve uncovered, LAPD Deputy Chief Michael Downing, who oversees the counterterrorism bureau, told the Times that this is a scenario officials have discussed for which they have attempted to create a response plan.

Marquez, who converted to Islam, was arrested and charged with conspiring to provide material support for crimes of terrorism for purchasing two AR-15 variants that were used by Farook and his accomplice wife Tashfeen Malik to carry out their massacre, along with two handguns bought by Farook.

Marquez reportedly stopped plotting the 2012 attack for a number of reasons, including fear stemming from the arrest of a group of men in Chino who were apprehended in an unrelated terrorism case, the documents show.

In recent years, the London, Madrid, Moscow, Paris, and Tokyo mass transportation systems have been the target of terrorist attacks. This past October, the Israel Defense Forces deployed 300 soldiers to Jerusalem to provide enhanced security for the capital’s endangered public transportation system, following a slew of knife attacks carried out by Palestinians and which targeted Jews.

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