An important issue for crowd safety is how long it would take to evacuate a venue. Like the last article this is not to attempting to figure out the exact right answer to how large entrance/exits need to be but to try see if someone with a limited knowledge and a search engine could easily see in advance that the entrance/exit to the love parade was dangerous. Even large venues can require evacuation in the case of a natural or manmade disaster. These disasters could be weather related as happened here here and here. In the case of man made safety risks venues also are sometimes evacuated. As described here
"On December 12, 2004, the stadium Santiago Bernabeu in Madrid was evacuated because of a bomb threat.... In eight minutes, more than 70,000 people left the premises without incident."
The respected Spiegel says
"Much of the critique has centered around the fact that the tunnel where the panic took place was the only entrance to and the only exit from the party site. "
If this tunnel was the only exit available (another tunnel seems to have been reserved for emergency vehicles) how quickly should people have been able to exit?
This soccer stadium with a capacity of over 25,000 claims 'The target evacuation time for the entire Stadium at full capacity is 8 minutes.'
This document on evacuation planning states
"The maximum Emergency Evacuation Time for sports ground varies between two and a half minutes and eight minutes"
Stadiums do not have as much free space as larger venues but they still allow for moving people onto the pitch as happened at a baseball game after the 1989 San Francisco earthquake. In the case of some natural disasters or terrorist threats a site wide evacuation might be needed so even large sites probably need to be able to be evacuated reasonably quickly.
The acceptable evacuation time for a stadium seems to be under ten minutes. If Spiegel is correct and this tunnel really was the only exit any evacuation would have taken hours which is not be acceptable.
The pictures here give a very good impression of what happened. The width of the tunnel does indeed look like 16 meters. And the 'ramp' described earlier just looks like something people tried to escape up rather than a designated route.