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Two cells of terrorists have rocked the United Kingdom, striking in the heart of its two greatest cities. As Americans look on in horror, with sympathy for our British allies, we wonder what lessons we should be taking so that we might avoid such events here. I see six relevant points.

First, some of the weapons being used are commonplace. As in Nice and Berlin, the London attack involved an everyday truck as the weapon, supplemented by kitchen knives. The absence of firearms in the hands of the terrorists is likely due to the United Kingdom’s strict gun laws. Were guns involved, as they easily could be here, the death tolls would have been higher. The point, however, is that terrorists are employing weapons they can easily access and there is little or nothing we can do to stop them from acquiring such items. Cities need to look anew at their streets and venues and consider what can be done to stop a vehicle from plowing into a cluster of civilians on a square, a pedestrian mall, or a row of sidewalk cafes. Simple countermeasures work. At this year’s Boston Marathon, I saw snow plows, dump trucks, and garbage trucks blocking side streets along the race route.

Second, areas around secure venues are often targets. Just as the Manchester bomber placed the lethal device just outside the secure area, other attackers have preyed on lines of people waiting to go through security checks or on facilities such as airline ticket counters just beyond secure zones. Police and security officials need to have both a visible (armed patrols and dogs) and an invisible (undercover behavioral spotters) presence in the “penumbra areas” near secure zones.