You should be able to walk away from most lava flows. However, recent videos of the lava flowing from an eruption of Kilauea in Hawaii shows rivers of lava flowing much much faster than this.
The speed of a lava flow is given for the very front of the lava; it’s assumed that once a lava has flowed over an area that no-one will be standing in the middle of a lava flow and therefore the speed there is not as important.
Before you get hot under the collar, the lava in these speedy lava rivers may travel around 60 km/hr (~ 40 mph), but the lava at the very front of the flow will travel only a few km or miles per hour.
However, there are exceptions. For example, lava flows from Nyiragongo, Africa, can travel at 60 km/hr (~40 mph) even at their very front. These lava flows are extremely dangerous as no-one can walk, or even run, fast enough to escape these.