Metro North Wreck: What Would it have cost to put up a "slow speed" warning sign?

Ms. Anders said on Monday that the tracks north of the station did not include any kind of marker telling engineers when to slow down. “Engineers are required to know maximum authorized speeds and speed restrictions as part of their territory qualification,” she said.... NY Times

Yes, the engineer should have known. But a simple flashing light would prevent the possibility of distraction. Thus the full blame will fall on the driver.