Tube passenger numbers have dropped by 30% at weekends and between 5% and 15% on weekdays, since the 7 July bombings, a senior manager has told BBC News.
Trains are now stopping at all Tube stations
Most regular commuters were continuing to travel - but a significant number of visitors and weekend shoppers were not using the system, the figures suggest.
The news comes as the Piccadilly Line reopens, and the Circle Line begins offering a limited service.
Managers said all stations were now being served.
They said the Piccadilly Line reopening marked an important day for the recovery of the Tube network.
Meanwhile, a massive police operation is under way across London's transport network and on its streets.
More than 6,000 officers, many armed, are expected to patrol stations and key sites.
A high-visibility presence will aim to make people feel safer while undercover officers mingle with commuters on the Tube and buses trying to spot potential bombers.
The Piccadilly Line had been suspended from Hyde Park Corner to Arnos Grove and from Rayners Lane to Uxbridge.
The tunnel between Russell Square and King's Cross stations has been a crime scene for much of the past month after a bomb on a train killed 26 people.
The Circle Line is running a shuttle service every 20 minutes between 0700 BST and 0900 BST and between 1600 BST and 1815 BST from Thursday, with the service expected to improve over the next few days.
The Hammersmith and City Line, also shut since 7 July, reopened on Tuesday.
I think it is very reassuring that we now have police at almost every station watching over us. It is important to send a strong message back to those sympathetic to terrorism against our country and others. I have 2 main problems with this move; why did they not organise security like this earlier? Even if it had not been on the same scale some form of terror prevention like this should have been implemented way back when we were first threatened by terrorists. And now we have police presence focused on terrorism, what about the other areas that need attention? Are they going to be ignored? It would be no good if street crimes and robberies went up, as people would then have other things to worry about.
Gedi Grudzinskas, London, England
My family and I are actually leaving today to come to London for a week. We have planned this trip for months. We do not plan on using the "Tube" and hope to enjoy the above ground taxis. A harsh reality for us but this is the way life is going to be. Our children, ages 10 and 16, do not understand the hate these terrorists have toward others. It has been challenging to explain real evil present in this world. But, we are looking forward to seeing jolly ole England!
Bob Doty, Oak Park, IL United States
For me the bombs were the straw that broke the camel's back - I will no longer use the tube. I always moaned about the fact that the tube was unreliable and over priced, but now that it is no longer safe, I'm happier using a bicycle to get about.
Alan Travis, London, England
If I can't get there by car or taxi, I don't go into London anymore. The web is providing a lot of my shopping needs. However, god knows what this is doing to London's retail economy. For the first time in my life, I am seriously considering emigrating elsewhere.
Helen, London (west London)
I have not been put off using the tube and will continue to use the tube regularly as long as I reside in London. I have no intention of allowing terrorism (or the fear of it) to change the way I live my life on a day to day basis.
O D Peterson, London, UK
The recent events have shocked and saddened me. I used to be a regular visitor to London for great shopping and vibrant theatre shows, but I now do not feel comfortable either visiting London, or using public transport. The emergency services have been brilliant over the past few weeks and the police presence is excellent, and what everybody needs at this time. However, this will not change my mind about using public transport.
Maz, Croydon, UK
I do not feel safe at all even with the police presence. I know I'm not the only one. I don't think I will ever use the tube again I'm sorry to say.
Dan Murrell, Essex
Along with most of the people who use the trains and underground, I have no choice but to use them as it is my only means of getting to work, and no-one is going to allow us time off because we are "afraid". I have to admit though that the presence of the police does make you feel a little easier on your travels. What is sad though is that I now view anyone with a backpack with suspicion and still feel fearful if someone sits near me while clutching one, and I have never had a problem with using public transport. How long though will it be before the Police presence disappears and we are once again alone on our travels? Or will the bombers select targets where the police are not so high profile? Or maybe even just change days after all the high presence is limited to Thursdays at the moment isn't it?
Carol Burton, Eastleigh, Hampshire
I used to travel to work by tube, since 7 July this option has not been open to me due to the closure of Piccadilly. I now travel all the way to work by bus from Walthamstow to Cockfosters which has added a lot of time to my journey. I might go back to tube travel in the winter when it starts getting cold, and the terror threat has calmed down a little. I used to come into the centre of London to meet friends after work and do some shopping but I have not done so since 7 July and I'm unlikely to do for sometime. The presence of police is reassuring, however I believe these terrorists will find a way as recent events show they are very capable.
Sue Nolan, Walthamstow
While the strong police presence is reassuring, I still feel that if the want is great enough, terrorists will still be able to carry out further attacks. I no longer travel by tube as a result.
Former Piccadilly Line Commuter, Herts
Due to the summer school holidays my daughter is with me all the time. I daren't travel on the tube because of the sense of panic that is prevalent. Even if a false alarm is raised a stampede could ensue and I am so afraid that my daughter will get caught up in it.
Jane Manning, London
I've started cycling to work instead of using the tube and bus. I always felt the tube was wide open to attack and was never really comfortable using it in recent years, the awful events of 7/7 made me get on my bike and I feel safer even in London's traffic.
Roger Stillman, London
I keep commuting to London and use the same trains and buses that I've done for over two years. If I get concerned about being injured by a bomb, I just tell myself that the risk is far less than been injured/killed in an accident if I had to travel any distance in a car each day.
Mr Stephen Hutton, Andover, Hampshire, England
The probability of being somewhere a bomb will explode is remote. However, one inevitably feels nervous, particularly in crowded confined places, with people with bags. I feel I am intimidating others if I carry my usual rucksack in crowded places, even though I am white skinned. What must it be like for those innocents with darker skin? The cowardly terrorist's weapons are blunt and indiscriminate.
Matyin Matthews, Hersham, UK
I commute to London. The bombs haven't stopped me using the tubes but the initial problems with the Circle Line made me realise it's actually quicker, easier and cheaper for me to cycle.
Paul Thurston, Cambridge, England
I had to travel to London on the Tuesday after the attacks, it meant a 2 mile walk to and from my destination but I walked rather than use the tubes or buses. I will walk from now on - or get a cab. I am not from London and have always hated the 'crowded and trapped underground' feeling of the tubes. Never again will I use them. I know this sounds weak and defeatist but I would rather be a live wimp than a dead hero.
I use the Central Line every day to get to work on Oxford Street, and was back using the tube the day after the bombings. I was a bit nervous at first, but not too nervous to use the tube. I have to get to work, I have no other choice. If it's my time it's my time. The police presence, if anything at all, makes me feel more nervous than safe.
I have changed my method of transport to work - being 7 months pregnant I didn't feel safe on the underground part of my journey on the tube so all of my journey is now over-ground by using overhead train and DLR. It takes an extra 10 or 15 minutes per day but it makes me feel better. I can see every day that the District Line from Barking onwards has seats - a month ago you couldn't even get on the tube - yet alone sit down - but maybe it's people like me who are still commuting into London - just changing their routes. We still have to work - we have no choice.