Monday marked the start of the annual United Nations General Assembly -- a.k.a. The annual gathering on Manhattan's east side triggers the city's yearly "Gridlock Alert" list, as security upgrades and a return trip by President Donald Trump will surely clog the streets all week long. Motorcades are the main reason for traffic headaches, as they crisscross the city while weaving in and out of traffic — including the usual marked green bike lanes. The bottom line: Avoid midtown if using streets in any way. The MTA urges using mass transit, though bus lanes will be squeezed in midtown, creating delays on those lines.