Turning the Bloor viaduct into a beacon of light in time for the Pan Am Games is going to cost nearly $3 million more than rough earlier projections suggested.

A Toronto staff report that will go to the city’s executive committee next week estimates the final price tag of lighting up the Prince Edward Viaduct with a cascade of changing colours and patterns will be nearly $4.7 million.

The higher-than-projected cost of the viaduct project stands in contrast to Toronto’s 10 Pan Am capital projects that are, for the most part, progressing on or under budget. The city has saved nearly $10 million on the Toronto Pan Am Sports Centre alone.

When a suicide barrier was erected on the viaduct in 2003, a “luminous veil” of coloured lights illuminating the Bloor St. E. heritage bridge from both top and bottom were part of the plan. But budget constraints got in the way and the more esthetic portions of the work weren’t completed.

Last year, an engineering firm provided a rough estimate of $1.8 million for the lighting project. Council added the project to Toronto’s $20-million showcase program, designed to enhance the city during the Games, and approved $200,000 to pay for designs, engineering work and detailed cost analysis. It also gave the green light to another $1.6 million to come from the 2014 budget if the project could be finished before the Games.

But original estimate was based on the concept proposal and other projects, rather than detailed design drawings or assessment of the conditions on the bridge, the report notes.

Now, city staff are calling for an additional $1 million to complete the first phase of the project in time for the Games and recommending the remaining $1.85 million needed for the second, final phase come from the 2015 capital budget. If all the funding’s OK’d by early 2015, the entire illumination project could be finished in time for the Games.

A spokesperson for the city said staff isn’t available to comment on the project until it’s discussed at executive committee on July 2. Coun. Paula Fletcher, a longtime champion of the project, said the $1.8 million in approved funding was never a final price tag.

“I think everybody understood that it was going to cost a bit more,” said Fletcher. “We didn’t know what the final amount was because none of the engineering had been done.”