Signs along Interstate 94 in St. Paul tell motorists which exits to use to get to popular destinations such as the Como Zoo and Conservatory, the Minnesota Children's Museum, the Ordway Center for the Arts and the Minnesota History Center.

Others direct drivers to the Xcel Energy Center, the State Capitol and schools such as the University of St. Thomas, Concordia University and Macalester College.

Carole, no last name given, has noticed them and she e-mailed The Drive to ask why most venues in St. Paul have signs along freeways while few museums, parks, schools and attractions in Minneapolis do.

Sure, there are signs for the soon-to-be-razed Metrodome, but conspicuously absent are signs guiding motorists to the Walker Art Center and Sculpture Garden, the Minneapolis Institute of Arts, Orchestra Hall or the theaters on Hennepin Avenue. Why?

The short answer is that venues must ask for them, and be willing to pay for them, said Josie Tayse, MnDOT's Metro District sign engineer. That might explain why there is a sign on westbound 94 for St. Mary's University but not for North Central University.

Any business or facility can ask for a sign, but MnDOT will grant their request only if certain criteria are met. For starters, the venue must be a major traffic generator and host several events a year, Tayse said. MnDOT also will grant signs to venues that attract people from out of town. That's why you'll see signs for airports, casinos, state parks and shopping centers. Small schools and colleges can have them, too.

MnDOT also has to determine if there is room on the freeway. According to MnDOT's Traffic Engineering Manual, guide signs must be placed close to the exit nearest to the attraction or school. The manual also says that guide signs must be placed a minimum of 800 feet apart so people can read and understand them before encountering the next one. "We don't want visual clutter, or one sign blocking another," Tayse said.

Assuming those criteria are met, the venue requesting a sign must pay for it. Sign fees begin at $850, but can quickly jump into the thousands depending on how big the sign is and how it is installed. The speed at which motorists will be passing will dictate how big the text needs to be so drivers can easily read the sign. The larger the text, the bigger the sign, and the more expensive it becomes.

MnDOT charges additional fees if it must hire a contractor to put the sign up. MnDOT crews can handle simple signs that are attached to a post driven into the ground. But since the agency does not have the equipment to affix signs to bridges or overhead structures such as the ones near Minneapolis-St. Paul International Airport that list the airlines and their respective terminals, MnDOT must call in outside help. That also drives the price up.

Tayse said MnDOT gets "quite a few" requests each year but was unsure how many requests resulted in new signs. She also said the two most common reasons that requests are denied are that the sign does not meet requirements or there isn't room for it.

A sign's messages determine its color. Green signs help drivers get somewhere: examples are shopping malls and stadiums. Blue is for motor services, such as for gas, lodging and food. Brown signs lead to recreation and historical sites such as Fort Snelling. Orange means trouble, as in road work and delays. □

Follow news about traffic and commuting at The Drive on startribune.com. Got traffic or transportation questions, or story ideas? E-mail drive@startribune.com, tweet @stribdrive or call Tim Harlow at 612-673-7768.