London, England (CNN) -- Tuesday marks two years to go until the London 2012 Olympics, the start of what organizing committee chief Sebastian Coe calls "the killing zone" -- the final stretch of an 800-meter race where you can see the finish line but still have to work to get there.
Coe, who won two Olympic gold and two silver medals in track and field, said recently he is preparing for "two very tough years" to make sure London can deliver the Games.
"This is the business end of the race now," he said. "You don't want to make errors, you don't want to make mistakes, you don't want to be off the pace, you want to know all the exit routes and all the strategies. You need to be very alert."
Coe said the Games are "on time and on budget," and he has few concerns that the world economic downturn will have an effect on preparations.
Unlike its sister organization, the Olympic Delivery Authority -- which is responsible for building venues and infrastructure -- the London Organizing Committee of the Olympic and Paralympic Games (LOCOG) is privately funded.
LOCOG has secured more than 85 percent of its hoped-for sponsorship money so far. There are now 34 Olympic sponsors and the committee wants to get more, Coe said, but finding them may be a challenge in the current economic climate.
"This hasn't been easy," he told CNN. "This has been a very, very difficult market. I don't think a Games has probably been delivered in a more taxing economic climate than probably the delivery of the Montreal Games in the early 1970s."
Some of the existing London sponsors have struggled. British Airways has been hurt by more than three weeks of strikes this year by its cabin crews, which threaten further walkouts over a still-unresolved dispute. Another top sponsor, BP, has faced global criticism for its part in and its handling of the Gulf of Mexico oil disaster.
Coe said he has no worries about BP as an Olympic partner and has been under no pressure to rethink its sponsorship.
"Absolutely not," he said. "They are a very valued, trusted, world-class business and I couldn't have wanted more from them," he told CNN.
Olympic venues are taking shape in the Olympic Park, the large site that is regenerating a formerly rundown area of the capital, and the first test events will be staged next May, Coe said.
Tuesday also marks the start of the London 2012 volunteering program. Organizers are looking for more than 70,000 people to staff everything from specialist positions like doctors and scoreboard operators to more general posts like ticket checking and uniform distribution.
Members of the International Olympic Committee visited London earlier this month and said transport is one issue that still needs to be fine-tuned. They mentioned London's narrow roads and the huge influx of cars into the city each day and said "creativity" is needed to make sure athletes and those involved in staging the Games can make it to the venues on time.
"I don't think we've ever been coy or naive about this," Coe said about the transportation issues. "We know London is a complex city. It's not based on the standard block or grid system that a lot of other European cities or world cities are, so it comes with its challenges. But actually, one great advantage of London, of course, is we are served very, very well by public transport, and we do have very smart partnerships and people in teams out there to help us figure that out."
Olympic transport officials were in South Africa for the recent World Cup to observe traffic plans there, Coe said.
Solving transportation issues is not on his list of worries, Coe said.
"If you're really pressing me (on worries), it's the things that you have no foresight on," he said, citing as an example the recent worldwide flight chaos caused by ash from an Icelandic volcano. "There are things that are beyond your control that you just don't know about."
In the past year, London 2012 unveiled its Olympic and Paralympic mascots -- one-eyed, futuristic figures designed to excite children about sports. Starting Tuesday, people can purchase the mascots and other Olympic merchandise at the new flagship store, opening at St. Pancras International train station in central London.
Tickets for the Games won't go on sale until next year, and organizers are still figuring out what prices to charge, Coe said. Ticket sales make up nearly a quarter of the organizing committee's budget, and in setting prices, organizers want to maximize their ticket revenue while still making tickets affordable, Coe said.
Coe has always highlighted the legacy he believes the Games will leave for London and the rest of the country, and he said it's something he remains proud of. The Olympic Park regeneration will leave 3,000 new homes, venues for top sporting events, and a large new green space in a former industrialized area.
He described it as "venues that Londoners have never had in a landscape that they wouldn't have risked walking their dogs on in a part of London that has been (a wasteland) for the past 170 years."
In an article published last week, The Economist magazine said the Games "look like an expensive way of refreshing the rundown end of town" and said the park risks being "an expensive flop."
Coe said he still believes the London Games will have lasting benefits.
"For me, the value for money and rate of return on investment, particularly given the fragility of the economy ... is one that I would be very happy to defend, and do," he told reporters Friday. "We have to continue to make very strong arguments that this is a project with national enormity. It's not coming around again in our lifetime."