This tactic if properly executed will completely lock down one fully enclosed city block in its entirety from all vehicles and most pedestrians (except for first responders) – from a few minutes to several hours.
The purposes for this type of traffic control are dynamic and used with other methods; trap or keep away a target, minimize witnesses, maximize operational maneuverability, delay or misdirect a pursuer / target, minimize collateral incidentals, create false positive crises and evasion.
It takes a single person to initiate within minutes or with an asset depending on the control systems. There’s no digital or network hacking, just manual operation with basic everyday tools.