SEATTLE — Tolling in Seattle's SR 99 tunnel started Saturday, but the true test will come on Tuesday, the first weekday commute following the long Veterans Day weekend. 

The question is how many drivers that have traveled free over the past 10 months may divert to surface streets or I-5 to avoid paying tolls. 

The impact could be significant. 

The Sounders MLS Cup championship game brought increased traffic to the Stadium District near the tunnel on Sunday. Yet, the Washington State Department of Transportation says traffic through the tunnel was down 35% compared to a typical two-day weekend. 

State and city transportation officials are prepared for a diversion rate of at least 30% and up to 50% of all the vehicles that previously used the tunnel.

"In general we expect that tolling is going to change traffic patterns, and that shift is going to be continuing in the months ahead," said SDOT spokesperson Ethan Bergerson. "It’s going to be a while before we see a new normal."

WSDOT officials said they have issued an additional 60,000 GoodToGo! passes since tunnel traffic went into effect, but only 35% of those passes have been activated as of this writing. 

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Heather Marx, with Seattle's transportation department, says the city is prepared to change stoplight timing and has eight additional police officers, plus an additional four city employees available, to help manage traffic if vehicles head for major north-south corridors such as 1st and 4th avenues. 

"What we've seen is exactly what we've expected to see," Marx said. "The true test is tomorrow (Tuesday), when it's a full commute."  

But Marx is also aware that it could be the full commute -- and then some -- as thousands of people are expected to head into Seattle to celebrate the Sounders championship win. 

RELATED: How to watch the Sounders MLS Cup victory parade and rally in Seattle on Tuesday

Wednesday and the rest of the week are likely to be a truer reflection of tolling's immediate impact. 

The next question is: How long will the diversions last?  

"It remains to be seen, but it could take months before things actually stabilize," according to WSDOT tolling chief Ed Barry.

RELATED: Seattle tunnel tolls now in effect: 5 things to know

Here’s a breakdown of the tolling schedule:

Weekdays:
6-7 a.m. – $1.25
7-9 a.m. – $1.50
9 a.m.-3 p.m. – $1.25
3-6 p.m. – $2.25
6-11 p.m. –$1.25
11 p.m.-6 a.m. – $1

Weekends: $1